JavaScript Basics and Advanced Concepts

A comprehensive guide covering client-side scripting basic and advanced JavaScript concepts

JavaScript Fundamentals

This document provides a comprehensive overview of JavaScript fundamentals, covering its history, basic concepts, data types, operators, control flow, functions, arrays, and objects.

History of JavaScript
Introduction to JavaScript
Using JavaScript in HTML
JavaScript Output
JavaScript Comments
Variables in JavaScript
Data Types in JavaScript
Operators and Expressions
Control Flow and Conditionals
Loops
Functions
Arrays
Objects
Unit 6 Questions for Exam Preparation
Scope and Closures
Error Handling and Debugging
DOM Manipulation
Asynchronous JavaScript
JSON and AJAX
ES6 and Modern JavaScript
JavaScript Libraries
Unit 7 Questions for Exam Preparation

1. History of JavaScript

JavaScript's history is rooted in the early days of the web.

1995: Created by Brendan Eich at Netscape Communications.
- Initially named LiveScript, later renamed to JavaScript to capitalize on Java's popularity.
JavaScript and Java are different languages despite similar names.
First appeared in Netscape Navigator 2.0 in 1995.
Designed to add interactivity to web pages.
Internet Explorer and other browsers quickly adopted JavaScript, making it a web development standard.
1996: Netscape submitted JavaScript to the European Computer Manufacturers Association (ECMA) for standardization.
- Standardized version named ECMAScript (officially ECMA-262).
ECMAScript is the official name, while JavaScript is the implementation of the standard.
ECMAScript ensures JavaScript works consistently across different browsers.
Evolution of JavaScript:
- ES3 (1999): Regular expressions, string handling, exception handling.
- ES5 (2009): Strict mode, JSON support, new array methods (map(), filter()).
- ES6 (2015): let and const, arrow functions, classes, modules, template literals; began annual updates.
- ES7 and Beyond: async/await (ES2017), optional chaining (ES2020), private class fields (ES2022).
JavaScript Today:
- Cornerstone of modern web development (front-end and back-end).
- Powers millions of websites and applications.
- Frameworks like React, Angular, and Vue.js have enhanced its versatility.
JavaScript and Oracle:
- JavaScript is a trademark of Oracle Corporation.
- An open standard guided by ECMA International.
Importance of ECMAScript:
- The official standard defining the JavaScript language.
- Ensures consistency and compatibility.
- JavaScript versions are often referred to by their ECMAScript version (e.g., ES6, ES2015).

2. Introduction to JavaScript

JavaScript adds interactivity to web pages.

It works with HTML (structure) and CSS (styling).
Used for:
- Dynamically updating content.
- Controlling multimedia.
- Animating images and graphics.
- Creating interactive features.
- Fetching and displaying data from servers without reloading pages.
Key Features:
- High-Level: Closer to human language than machine language.
- Interpreted: Executed line by line by the browser's JavaScript engine.
- Lightweight: Fast and efficient for interactive web pages.
- Case-Sensitive: myVariable is different from myvariable.
- Object-Based: Centered around objects.
Why Learn JavaScript?
- Front-End Development: Interactive and dynamic user interfaces.
- Back-End Development: Server-side programming with Node.js.
- Cross-Platform Development: Mobile apps with React Native and desktop apps with Electron.
- High Demand: Popular language with a large demand for skilled developers.

First JavaScript Code:

console.log("Hello World!"); // Output: Hello World!

JavaScript in Action:
- Form validation.
- Interactive maps.
- Dynamic content updates.
- Web page animations.

3. Using JavaScript in HTML

JavaScript is added to HTML in three ways:

Inline JavaScript:
- JavaScript code directly in HTML elements via event attributes (onclick, onload, etc.).
- Useful for small tasks but discouraged for larger projects.
```
<button onclick="document.getElementById('demo').innerHTML = Date()">
  The time is?
</button>
```

Internal JavaScript:

JavaScript code inside <script> tags within the HTML document.
Useful for small scripts specific to a single page.

<body>
  <h1>My First Web Page</h1>
  <p id="demo">This is a paragraph.</p>
  <button
    type="button"
    onclick="document.getElementById('demo').innerHTML = Date()"
  >
    Click me to display Date and Time.
  </button>
  <script>
    console.log("Hello World!");
  </script>
</body>

External JavaScript:

JavaScript code in a separate file linked to the HTML document using <script> tag with a src attribute.
Best method for larger projects to keep HTML and JavaScript code separate.

<body>
  <h1>My First Web Page</h1>
  <p id="demo">This is a paragraph.</p>
  <button
    type="button"
    onclick="document.getElementById('demo').innerHTML = Date()"
  >
    Click me to display Date and Time.
  </button>
  <script src="myScript.js"></script>
</body>

myScript.js will contain the Javascript code.

Best Practices:
- Use Inline JavaScript sparingly.
- Use Internal JavaScript for small, page-specific scripts.
- Use External JavaScript for larger projects.
- Place <script> tags at the end of the <body> section to ensure HTML content loads before JavaScript runs.

4. JavaScript Output

JavaScript outputs data in several ways:

Writing into an HTML Element (innerHTML):

Inserts or modifies content within an HTML element.

<p id="demo"></p>
<script>
  document.getElementById("demo").innerHTML = 5 + 6;
</script>

Writing into HTML Output (document.write()):
- Writes content directly into the HTML document.
- Use sparingly, as it can overwrite the entire document.
```
<script>
  document.write(5 + 6);
</script>
```
Writing into an Alert Box (window.alert()):
- Displays a pop-up alert box with a message.
- Useful for debugging or notifications.
```
<script>
  window.alert(5 + 6);
</script>
```
Writing into the Browser Console (console.log()):
- Outputs data to the browser's console.
- Used for debugging and testing.
```
console.log(5 + 6);
```

Practical Use Cases:
- innerHTML for dynamic content updates.
- document.write() for quick testing (avoid in production).
- window.alert() for small notifications or debugging.
- console.log() for debugging.

5. JavaScript Comments

Comments explain JavaScript code, making it easier to understand.

Single-Line Comments (//):

Text between // and the end of the line is ignored.

let greeting = "Hello, World!"; // This variable stores a greeting message
console.log(greeting); // Output: Hello, World!

Multi-Line Comments (/* ... */):

Text between /* and */ is ignored.
Useful for longer explanations or disabling code blocks.

/*
  The following code calculates the sum of two numbers
  and logs the result to the console.
*/
let num1 = 10;
let num2 = 20;
let sum = num1 + num2;
console.log(sum); // Output: 30

Best Practices:
- Explain the "why" behind the code, not the "what".
- Keep comments concise and relevant.
- Avoid over-commenting.
- Update comments when you update the code.
- Use single-line comments for short explanations and multi-line comments for longer blocks.
Debugging:
- Comments are used to temporarily disable code during debugging.

Special Cases:

Comments can also be used in template literals to comment out HTML or CSS inside JavaScript.

let htmlContent = `
    <div>
      <h1>Hello, World!</h1>
      <!-- <p>This paragraph is commented out.</p> -->
    </div>
  `;
let cssContent = `
    .container {
      width: 100%;
      /* height: 200px; */
    }
  `;

6. Variables in JavaScript

Variables store data used throughout a program.

Declaration keywords: var, let, const.

var (Function-scoped):

Oldest way to declare variables.
Function-scoped; globally scoped if outside a function.
Allows redeclaration and reassignment.

var greeting = "Hello, World!";
console.log(greeting); // Output: Hello, World!

var greeting = "Hi there!";
console.log(greeting); // Output: Hi there!

greeting = "How are you?";
console.log(greeting); // Output: How are you?

let (Block-scoped):

Introduced in ES6.
Block-scoped (accessible within a block: {}).
Allows reassignment but not redeclaration within the same scope.

let count = 10;
console.log(count); // Output: 10

count = 20;
console.log(count); // Output: 20

if (true) {
  let blockScoped = "I am inside a block";
  console.log(blockScoped); // Output: I am inside a block
}

const (Block-scoped, Immutable):

Introduced in ES6.
Block-scoped and cannot be reassigned.
Must be initialized at declaration.

const PI = 3.14159;
console.log(PI); // Output: 3.14159

// const PI = 3.14; // Error

For objects and arrays, const only prevents reassignment of the variable, not the contents of the object/array.

const person = {
  name: "Alice",
  age: 25,
};
person.age = 26; // Allowed
console.log(person); // Output: { name: 'Alice', age: 26 }

Variable Naming Rules:
- Letters, digits, underscores (_), and dollar signs ($).
- Must begin with a letter, underscore, or dollar sign (not a digit).
- Case-sensitive.
- Reserved keywords cannot be used.
Best Practices:
- Use const by default. Use let for values that will change.
- Avoid var.
- Use descriptive names.
- Follow a consistent naming convention (camelCase).

7. Data Types in JavaScript

JavaScript variables hold various data types, categorized as:

Primitive Data Types: String, Number, Boolean, Undefined, Null, BigInt, Symbol.
Reference Data Types: Object, Array, Function.

1. Primitive Data Types:

String: Textual data.

var name = "John";
console.log(name); // Output: John
console.log(typeof name); // Output: string

Number: Numeric data (integers, floats).

var age = 25;
console.log(age); // Output: 25
console.log(typeof age); // Output: number

Boolean: Logical values (true or false).

var isStudent = true;
console.log(isStudent); // Output: true
console.log(typeof isStudent); // Output: boolean

Undefined: Variable declared but not assigned a value.

var address;
console.log(address); // Output: undefined
console.log(typeof address); // Output: undefined

Null: Intentional absence of any object value.

var car = null;
console.log(car); // Output: null
console.log(typeof car); // Output: object (quirk of JS)

BigInt: Integers larger than 2^53 - 1.

var bigNumber = 9007199254740991n;
console.log(bigNumber); // Output: 9007199254740991n
console.log(typeof bigNumber); // Output: bigint

Symbol: Unique and immutable value.

var id = Symbol("id");
console.log(id); // Output: Symbol(id)
console.log(typeof id); // Output: symbol

2. Reference Data Types:

Object: Key-value pairs.

var person = {
  firstName: "Jane",
  lastName: "Doe",
  age: 30,
};
console.log(person);
console.log(typeof person); // Output: object

Array: Ordered list of values.

var colors = ["Red", "Green", "Blue"];
console.log(colors);
console.log(typeof colors); // Output: object (Arrays are a type of object)

Function: Block of code for a specific task.

function greet() {
  console.log("Hello, World!");
}
console.log(greet); // Output: [Function: greet]
console.log(typeof greet); // Output: function

String Indexing:

Access characters in a string using their index (0-based).

var greeting = "Hello";
console.log(greeting[0]); // Output: H
console.log(greeting.charAt(1)); // Output: e

String Methods:

length: Returns the length of the string.

console.log(greeting.length); // Output: 5

toUpperCase(), toLowerCase(): Converts the string to upper or lower case.

console.log(greeting.toUpperCase()); // Output: HELLO
console.log(greeting.toLowerCase()); // Output: hello

indexOf(), lastIndexOf(): Finds the index of a substring.

console.log(greeting.indexOf("l")); // Output: 2
console.log(greeting.lastIndexOf("l")); // Output: 3

slice(), substring(), substr(): Extracts a part of the string.

console.log(greeting.slice(1, 4)); // Output: ell
console.log(greeting.substring(1, 4)); // Output: ell
console.log(greeting.substr(1, 3)); // Output: ell

replace(): Replaces a substring with another string.

console.log(greeting.replace("Hello", "Hi")); // Output: Hi

split(): Splits the string into an array of substrings.

console.log(greeting.split("")); // Output: ["H", "e", "l", "l", "o"]

Type Conversion:

Convert values to strings using String(), toString(), or template literals.

var num = 10;
console.log(String(num)); // Output: "10"
console.log(num.toString()); // Output: "10"
console.log(`${num}`); // Output: "10"

String Concatenation:

Combine strings using the + operator or concat() method.

var firstName = "John";
var lastName = "Doe";
var fullName = firstName + " " + lastName; // Output: "John Doe"
console.log(fullName);
console.log(firstName.concat(" ", lastName)); // Output: "John Doe"

Template Strings:

Use backticks (`) for template literals, allowing for easier string interpolation.

var age = 25;
var message = `Hello, my name is ${name} and I am ${age} years old.`;
console.log(message); // Output: Hello, my name is John and I am 25 years old.

8. Operators and Expressions

Operators perform operations on values, while expressions evaluate to a single value.

Types of Operators:

Arithmetic Operators:
- + (Addition)
- - (Subtraction)
- * (Multiplication)
- / (Division)
- % (Modulus)
- ** (Exponentiation)

let sum = 10 + 5; // Addition: 15
let difference = 10 - 5; // Subtraction: 5
let product = 10 * 5; // Multiplication: 50
let quotient = 10 / 5; // Division: 2
let remainder = 10 % 3; // Modulus: 1
let power = 2 ** 3; // Exponentiation: 8

Assignment Operators:
- = (Assign)
- += (Add and assign)
- -= (Subtract and assign)
- *= (Multiply and assign)
- /= (Divide and assign)
- %= (Modulus and assign)

let x = 10;
x += 5; // x = 15
x -= 3; // x = 12
x *= 2; // x = 24
x /= 4; // x = 6
x %= 5; // x = 1

Comparison Operators:
- == (Equal to, value only)
- === (Equal to, value and type)
- != (Not equal to, value only)
- !== (Not equal to, value and type)
- > (Greater than)
- < (Less than)
- >= (Greater than or equal to)
- <= (Less than or equal to)

let a = 10;
let b = "10";
console.log(a == b); // true (value is the same)
console.log(a === b); // false (value and type are different)
console.log(a != b); // false
console.log(a !== b); // true

Logical Operators:
- && (Logical AND)
- || (Logical OR)
- ! (Logical NOT)

let isStudent = true;
let isAdult = false;
console.log(isStudent && isAdult); // false
console.log(isStudent || isAdult); // true
console.log(!isStudent); // false

Bitwise Operators:
- & (Bitwise AND)
- | (Bitwise OR)
- ^ (Bitwise XOR)
- ~ (Bitwise NOT)
- << (Left shift)
- >> (Right shift)
- >>> (Unsigned right shift)

let num1 = 5;
let num2 = 3;
console.log(num1 & num2); // 1
console.log(num1 | num2); // 7
console.log(num1 ^ num2); // 6

String Operators:
- + (Concatenation)

let firstName = "John";
let lastName = "Doe";
let fullName = firstName + " " + lastName; // "John Doe"

Conditional (Ternary) Operator:
- condition ? expression1 : expression2

let age = 18;
let status = age >= 18 ? "Adult" : "Minor"; // "Adult"

Unary Operators:
- ++ (Increment)
- -- (Decrement)
- typeof (Type check)
- delete (Delete property)

let count = 5;
count++;
count--;
console.log(typeof count);

Type Operators:
- typeof
- instanceof

console.log(typeof "Hello"); // "string"
console.log(typeof 10); // "number"
console.log(typeof true); // "boolean"

Expressions: Combinations of values, variables, operators, and function calls.

let result = 10 + 5 * 2;
let isEligible = age >= 18 && isStudent;
let message = "Hello, " + firstName;

9. Control Flow and Conditionals

Control flow is the order of statement execution; conditionals make decisions based on conditions.

if Statements:

Executes code if the condition is true.

let age = 18;
if (age >= 18) {
  console.log("You are an adult.");
}

else Statements:

Executes code if the if condition is false.

let temperature = 25;
if (temperature > 30) {
  console.log("It's hot outside.");
} else {
  console.log("It's not hot outside.");
}

else if Statements:

Tests multiple conditions.

let score = 85;
if (score >= 90) {
  console.log("Grade: A");
} else if (score >= 80) {
  console.log("Grade: B");
} else if (score >= 70) {
  console.log("Grade: C");
} else {
  console.log("Grade: F");
}

switch Statements:

Performs actions based on different conditions.

let day = "Monday";
switch (day) {
  case "Monday":
    console.log("Today is Monday.");
    break;
  case "Tuesday":
    console.log("Today is Tuesday.");
    break;
  default:
    console.log("Today is not Monday or Tuesday.");
}

Ternary Operator (Conditional Operator):

Shorthand for if-else statements.

let isRaining = true;
let weatherMessage = isRaining
  ? "Bring an umbrella."
  : "Enjoy the weather.";
console.log(weatherMessage);

Nested Conditionals: Conditionals within other conditionals for complex logic.

let num = 10;
if (num > 0) {
  if (num % 2 === 0) {
    console.log("The number is positive and even.");
  } else {
    console.log("The number is positive and odd.");
  }
} else {
  console.log("The number is not positive.");
}

10. Loops

Loops execute a block of code repeatedly.

for Loop:

When the number of iterations is known.

for (let i = 0; i < 5; i++) {
  console.log("Iteration:", i);
}

while Loop:

As long as a condition is true.

let count = 0;
while (count < 5) {
  console.log("Count:", count);
  count++;
}

do...while Loop:

Executes code at least once, then as long as the condition is true.

let num = 0;
do {
  console.log("Number:", num);
  num++;
} while (num < 0);

for...in Loop:

Iterates over object properties.

const person = {
  name: "John",
  age: 30,
  occupation: "Developer",
};

for (let key in person) {
  console.log(key + ":", person[key]);
}

for...of Loop:

Iterates over iterable objects (arrays, strings).

const colors = ["Red", "Green", "Blue"];
for (let color of colors) {
  console.log("Color:", color);
}

Loop Control Statements:

break: Exits the loop immediately.
continue: Skips the current iteration and moves to the next.

for (let i = 0; i < 10; i++) {
  if (i === 5) {
    break;
  }
  if (i % 2 === 0) {
    continue;
  }
  console.log("Odd Number:", i);
}

11. Functions

Functions are reusable code blocks.

Function Declaration:

Named function with function keyword.

function greet(name) {
  return "Hello, " + name + "!";
}

console.log(greet("John"));

Function Expression:

Function assigned to a variable.

const greetUser = function (name) {
  return "Hello, " + name + "!";
};

console.log(greetUser("Alice"));

Arrow Functions:

Concise way to write functions (ES6).

const greetPerson = (name) => {
  return "Hello, " + name + "!";
};
console.log(greetPerson("Bob"));

const add = (a, b) => a + b;
console.log(add(2, 3)); // Output: 5

Parameters and Arguments:

Parameters: Variables listed in the function definition.
Arguments: Actual values passed to the function.

function multiply(a, b) {
  return a * b;
}
console.log(multiply(4, 5));

function sayHello(name = "Guest") {
  return "Hello, " + name + "!";
}
console.log(sayHello());
console.log(sayHello("Emily"));

Return Statement: Specifies the value to return from a function.

function checkAge(age) {
  if (age >= 18) {
    return "Adult";
  } else {
    return "Minor";
  }
}
console.log(checkAge(20));

Function Scope:

Variables inside a function are local to that function.

function myFunction() {
  let message = "Hello, World!";
  console.log(message);
}

Higher-Order Functions:

Functions that accept functions as arguments or return functions.

function operate(a, b, operation) {
  return operation(a, b);
}

function add(x, y) {
  return x + y;
}

function multiply(x, y) {
  return x * y;
}
console.log(operate(2, 3, add));
console.log(operate(2, 3, multiply));

Callback Functions:

Functions passed as arguments to other functions and executed later.

function greetUser(name, callback) {
  console.log("Hello, " + name + "!");
  callback();
}
function sayGoodbye() {
  console.log("Goodbye!");
}
greetUser("John", sayGoodbye);

Immediately Invoked Function Expressions (IIFE):
- Functions executed immediately after they are defined.
```
(function () {
  console.log("This is an IIFE!");
})();
```

12. Arrays

Arrays are used to store collections of values.

Creating Arrays:

Array literals or Array constructor.

let fruits = ["Apple", "Banana", "Orange"];
let numbers = new Array(1, 2, 3, 4, 5);

Accessing Elements:
- Using their index (0-based).
```
console.log(fruits[0]);
```
Modifying Elements:
- Assign a new value to a specific index.
```
fruits[1] = "Mango";
```
Array Length:
- The length property.
```
console.log(fruits.length);
```
Adding/Removing Elements:
- push(): Adds to the end.
- pop(): Removes from the end.
- unshift(): Adds to the beginning.
- shift(): Removes from the beginning.
```
fruits.push("Grapes");
fruits.pop();
fruits.unshift("Pineapple");
fruits.shift();
```

Iterating Over Arrays:

for loop
forEach()
for...of loop

for (let i = 0; i < fruits.length; i++) {
  console.log(fruits[i]);
}
fruits.forEach(function (fruit) {
  console.log(fruit);
});
for (let fruit of fruits) {
  console.log(fruit);
}

Common Array Methods:
- concat(): Combines arrays.
- slice(): Returns a portion.
- splice(): Adds or removes elements at a specific index.
- indexOf(): Returns the index of the first occurrence of a value.
- includes(): Checks if an array contains a specific value.
- join(): Joins elements into a string.
- reverse(): Reverses the order of elements.
- sort(): Sorts the elements.
```
let moreFruits = ["Grapes", "Pineapple"];
let allFruits = fruits.concat(moreFruits);
let citrus = fruits.slice(1, 3);
fruits.splice(1, 1, "Strawberry");
console.log(fruits.indexOf("Orange"));
console.log(fruits.includes("Apple"));
let fruitString = fruits.join(", ");
fruits.reverse();
fruits.sort();
```

Multidimensional Arrays:

Arrays containing other arrays.

let matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
];
console.log(matrix[1][2]);

Array Destructuring:
- Unpack values from arrays into distinct variables.
```
let [firstFruit, secondFruit] = fruits;
```

13. Objects

Objects store collections of key-value pairs.

Creating Objects:

Object literals or Object constructor.

let person = {
  name: "John",
  age: 30,
  occupation: "Developer",
};
let car = new Object();
car.make = "Toyota";
car.model = "Camry";
car.year = 2020;

Accessing Properties:

Dot notation or bracket notation.

console.log(person.name);
console.log(person["age"]);
let key = "occupation";
console.log(person[key]);

Modifying Properties:
- Assign a new value to the property.
```
person.age = 31;
person.city = "New York";
```
Deleting Properties:
- Using the delete operator.
```
delete person.city;
```

Object Methods:

Functions stored as object properties.

let person2 = {
  name: "Alice",
  age: 25,
  greet: function () {
    return "Hello, my name is " + this.name + "!";
  },
};
console.log(person2.greet());
let person3 = {
  name: "Bob",
  age: 28,
  greet() {
    return "Hi, I'm " + this.name + "!";
  },
};
console.log(person3.greet());

The this Keyword:

Refers to the current object.

let person4 = {
  name: "Emily",
  age: 22,
  introduce() {
    return (
      "My name is " + this.name + " and I'm " + this.age + " years old."
    );
  },
};
console.log(person4.introduce());

Nested Objects:

Objects can contain other objects.

let student = {
  name: "Mike",
  age: 20,
  address: {
    city: "Los Angeles",
    state: "California",
  },
};
console.log(student.address.city);

Object Destructuring:

Unpack properties from objects into distinct variables.

let { name, age } = person;
let { name: fullName, age: years } = person;

Iterating Over Objects:

for...in loop
Object.keys(): Returns keys as an array
Object.values(): Returns values as an array
Object.entries(): Returns key-value pairs as an array

for (let key in person) {
  console.log(key + ": " + person[key]);
}
let keys = Object.keys(person);
let values = Object.values(person);
let entries = Object.entries(person);

Object Prototypes:

Objects inherit properties and methods from their prototype.

function Person(name, age) {
  this.name = name;
  this.age = age;
}

Person.prototype.greet = function () {
  return "Hello, my name is " + this.name + "!";
};

let person5 = new Person("Sarah", 29);
console.log(person5.greet());

Unit 6 Questions for Exam Preparation

Note
Refer to all old and model questions and solve them.
This is crucial for exam preparation as these questions are directly aligned with the syllabus and have been tested in previous exams. Make sure to practice them thoroughly!

Introduction to JavaScript

How does JavaScript add interactivity to web pages?
Explain why learning JavaScript is beneficial for front-end development.
Provide an example of a simple JavaScript code that outputs "Hello World!" to the console.
What makes JavaScript a high-level language?
List three main use cases of JavaScript.
Why is JavaScript considered "lightweight"?
What does it mean that JavaScript is "case-sensitive"?
How does console.log() help in development?

Using JavaScript in HTML

Describe three ways to add JavaScript to an HTML document.
Why is it recommended to place <script> tags at the end of the <body> section?
Why is external JavaScript preferred for larger projects?
What is the difference between inline and internal JavaScript?
How do you link an external JavaScript file in HTML?
What happens if you place <script> tags in the <head> section of an HTML document?

JavaScript Output

List and describe four ways to output data in JavaScript.
Why should document.write() avoid while writing JavaScript code?
When should you use innerHTML versus document.write()?
What is the main purpose of console.log()?
How do you display a pop-up message using JavaScript?
What is the difference between alert() and console.log()?
What is a prompt box? - (Fall 2023, Q6)

JavaScript Comments

What is the difference between single-line and multi-line comments in JavaScript?
Provide an example of how comments can be used to temporarily disable code during debugging.
What is the best practice for using comments in JavaScript?
How do you write a comment in a template literal?

Variables in JavaScript

Compare and contrast var, let, and const in JavaScript.
Provide an example of a variable declared using const and explain what happens if you try to reassign it.
Why is const preferred for values that won't change?
Explain block scope versus function scope.
What are the rules for naming variables in JavaScript?
What is variable hoisting, and how does it affect var declarations?

Data Types in JavaScript

List and describe the all primitive and reference data types in JavaScript.
How do you check the type of a variable in JavaScript?
Provide an example of an object and an array in JavaScript.
What is the difference between null and undefined?
What is type coercion in JavaScript?
Explain the difference between reference and primitive data types.
What is the difference between undefined value and null value? (Model Question, Q7)

Operators and Expressions

What are arithmetic operators? Provide examples.
Explain the difference between == and === operators.
What is the purpose of the ternary operator? Provide an example.
List three types of logical operators.
What is operator precedence?
How do you use the spread operator?
Explain types of operator in JS? Explain in detail. (Spring 2024, Q12)
Explain types of JavaScript operators in detail. Use examples to demonstrate. (Model Question, Q15)

Control Flow and Conditionals

Describe how an if statement works in JavaScript.
Provide an example of a switch statement that handles different days of the week.
When would you use a switch statement instead of if-else?
What is the difference between break and continue?
How can you chain multiple conditions using else if?
What is the advantage of using a ternary operator?
How do you handle multiple conditions with logical operators?
Write a JavaScript function to calculate the grade of a student based on the mark. (Fall 2023, Q14; Model Question, Q17)
Explain how error handling is done using try-catch blocks in JavaScript. (Spring 2024, Q14b)

Loops

Compare and contrast for, while, and do...while loops.
What is the purpose of the break and continue statements in loops?
What is the difference between while and do...while loops?
When would you use for...in versus for...of?
How do you break out of a nested loop?
What is an infinite loop, and how do you avoid it?
How do you iterate over an array using different types of loops?
Write an example of a for...in loop to iterate over object properties.
Develop a JavaScript function that iterates through an array of numbers, separates prime numbers and composite numbers into different arrays and returns them as an object. (Fall 2023, Q17b)

Functions

What is the difference between a function declaration and a function expression?
Provide an example of an arrow function and explain its syntax.
How do higher-order functions work? Provide an example.
What is the difference between function declarations and expressions?
How do arrow functions differ from regular functions?
Explain function hoisting.
What are higher-order functions?
How do callback functions work?
Define callback function. (Fall 2023, Q7; Spring 2024, Q8)
What are arrow functions? (Fall 2023, Q17a)

Arrays

How do you create an array in JavaScript? Provide two methods.
List three methods to add or remove elements from an array and provide examples.
What is array destructuring? Provide an example.
How do you sort an array of numbers?
What is the difference between slice() and splice()?
Explain any two uses of arrays in JavaScript. (Model Question, Q8)
Develop a JavaScript function that iterates through an array of numbers... (Fall 2023, Q17b)

Objects

How do you create an object in JavaScript? Provide two methods.
Explain how to access and modify object properties.
What is the this keyword, and how is it used in object methods? Provide an example.
How do you loop through object properties?
What is object destructuring?
How do prototypes work in JavaScript?
What is JSON? When is it used? (Spring 2024, Q10)
Develop a JavaScript function that returns an object with prime and composite numbers. (Fall 2023, Q17b)

It looks like you're asking for the complete content of Unit 7, which includes advanced JavaScript concepts such as scope and closures, error handling and debugging, DOM manipulation, asynchronous JavaScript, JSON and AJAX, ES6 and modern JavaScript, and JavaScript libraries. Below is the comprehensive content for Unit 7:

Unit 7: Advanced JavaScript Concepts

1. Scope and Closures

Scope

Scope determines the accessibility of variables, functions, and objects in different parts of your code. It controls where a variable can be accessed or modified.

Global Scope

Variables declared outside any function have a global scope. They can be accessed and modified from anywhere in your code.

let globalVariable = "I am global!"; // Declared in the global scope
function checkGlobal() {
  console.log(globalVariable); // Accessing a global variable inside a function
}
checkGlobal(); // Output: I am global!
console.log(globalVariable); // Accessing a global variable outside a function

Local (Function) Scope

Variables declared inside a function have a local scope. They can only be accessed and modified within that function.

function myFunction() {
  let localVariable = "I am local!"; // Declared in the function scope
  console.log(localVariable); // Accessing a local variable
}
myFunction(); // Output: I am local!
// console.log(localVariable); // Error: localVariable is not defined (outside of myFunction)

Block Scope

Variables declared with let and const have block scope, meaning they are only accessible within the block (e.g., inside if statements, for loops, or {}).

if (true) {
  let blockScoped = "I am block-scoped!";
  console.log(blockScoped); // Output: I am block-scoped!
}
// console.log(blockScoped); // Error: blockScoped is not defined

Closures

A closure is created when an inner function attempts to access the scope of its outer function even after the outer function has completed its execution. The inner function "remembers" the environment in which it was created.

function outerFunction(outerVariable) {
  return function innerFunction(innerVariable) {
    console.log(outerVariable); // Accessing outer variable
    console.log(innerVariable); // Accessing inner variable
  };
}
let myClosure = outerFunction("Hello from outer");
myClosure("Hello from inner"); // Output: Hello from outer
// Hello from inner

Uses of Closures

Closures are commonly used in:

Data Encapsulation: To hide data and provide a controlled interface.
Creating Private Variables.
Implementing Callbacks and Event Handlers.
Creating Function Factories: Functions that return other functions.

function createCounter() {
  let count = 0; // Private variable
  return {
    increment: function () {
      count++;
    },
    getCount: function () {
      return count;
    },
  };
}
let counter = createCounter();
counter.increment();
console.log(counter.getCount()); // Output: 1
counter.increment();
console.log(counter.getCount()); // Output: 2
// console.log(count); // Error: count is not defined because it's inside createCounter.

Key Takeaways for Students

Scope determines where variables can be accessed.
Global scope variables are accessible everywhere.
Local (function) scope variables are only accessible within the function.
Block scope variables (with let and const) are only accessible within their block.
Closures allow inner functions to remember and access their outer function's scope, even after the outer function has completed.
Closures are crucial for data encapsulation, private variables, and many other advanced JavaScript patterns.

2. Error Handling and Debugging

Error handling is essential for building robust applications that handle unexpected situations gracefully. Debugging is the process of identifying and fixing errors in your code.

Types of Errors

JavaScript has several types of errors:

Syntax Errors: Occur when JavaScript syntax rules are violated.
Runtime Errors: Occur during execution of code, such as trying to access an undefined variable or dividing by zero.
Logical Errors: Occur when the code runs without crashing but doesn't produce the expected outcome due to logic errors.

// Syntax Error
// let myVar // SyntaxError: Missing semicolon

// Runtime Error
let num = undefined;
console.log(num.toLowerCase()); // TypeError: Cannot read property 'toLowerCase' of undefined

// Logical Error
function add(a, b) {
  return a - b; // Logical error: should be a + b
}
let result = add(5, 3); // Result: 2 (should be 8)

`try...catch` Statement

The try...catch statement allows you to handle errors by trying a block of code and catching any errors that occur.

try {
  // Code that might throw an error
  let num = undefined;
  console.log(num.toLowerCase());
} catch (error) {
  // Code to handle the error
  console.error("An error occurred:", error.message); // Output: An error occurred: Cannot read properties of undefined (reading 'toLowerCase')
} finally {
  // Code that will execute regardless of success or failure
  console.log("Finally block executed");
}

Throwing Errors

You can also throw custom errors using the throw statement, which is useful for handling invalid data or unexpected conditions.

function checkAge(age) {
  if (age < 0) {
    throw new Error("Age cannot be negative!");
  }
  return "Age is valid";
}

try {
  let result = checkAge(-5);
  console.log(result);
} catch (error) {
  console.error("Error:", error.message); // Output: Error: Age cannot be negative!
}

Debugging Techniques

Debugging is the process of finding and fixing errors in your code. Here are some techniques:

Using console.log(): Logging variables and messages to the console for debugging.
Using Browser Debugger: Step through code, set breakpoints, inspect variables, and monitor the program's state.
Using debugger Statement: Insert debugger; in your code to pause execution at that point.

function calculateSum(a, b) {
  let sum = a + b;
  debugger; // Pauses code execution to inspect variables
  return sum;
}

Error Object

The Error object provides information about an error that occurred. Key properties include:

message: Error message text.
name: Error type (e.g., "TypeError", "ReferenceError").
stack: Stack trace of where the error occurred.

Key Takeaways for Students

Error handling is vital for creating stable and user-friendly applications.
Use try...catch blocks to catch and handle errors that might occur during code execution.
Use the throw statement to raise custom errors based on specific conditions.
Debugging is a key skill in software development; use debugging tools effectively.
The Error object provides properties such as message, name, and stack.

3. DOM Manipulation

The Document Object Model (DOM) is a programming interface for HTML and XML documents. It represents the document as a tree-like structure of objects. JavaScript can use the DOM to interact with HTML elements, modify their content, style, and behavior.

Understanding the DOM

The DOM is an object-based representation of the HTML structure. Each HTML tag, attribute, and text node is represented as a node in the DOM tree. The document object serves as the entry point to access the DOM.

<html>
  <head>
    <title>My Page</title>
  </head>
  <body>
    <h1 id="title">Welcome</h1>
    <p class="content">This is some content.</p>
    <button onclick="handleClick()">Click me</button>
  </body>
</html>

Selecting Elements

JavaScript provides methods to select HTML elements:

getElementById(): Selects elements by ID.
getElementsByClassName(): Selects elements by class name (returns an HTML collection).
getElementsByTagName(): Selects elements by tag name (returns an HTML collection).
querySelector(): Selects the first element that matches the CSS selector.
querySelectorAll(): Selects all elements that match the CSS selector (returns a NodeList).

// Selecting by ID
let titleElement = document.getElementById("title");
console.log(titleElement); // Output: <h1 id="title">Welcome</h1>

// Selecting by class name
let contentElements = document.getElementsByClassName("content");
console.log(contentElements); // Output: HTMLCollection(1) [p.content]

// Selecting by tag name
let pElements = document.getElementsByTagName("p");
console.log(pElements); // Output: HTMLCollection(1) [p.content]

// Selecting by CSS selector (single)
let element1 = document.querySelector(".content");
console.log(element1); // Output: <p class="content">This is some content.</p>

// Selecting by CSS selector (multiple)
let element2 = document.querySelectorAll("p");
console.log(element2); // Output: NodeList(1) [p.content]

Modifying Elements

Once selected, you can modify element properties:

innerHTML: Sets the inner HTML content of an element.
textContent: Sets the text content of an element.
setAttribute(): Sets the value of an attribute.
style: Sets the inline style of an element.
classList: Adds, removes, or toggles CSS classes.

// Modifying innerHTML
titleElement.innerHTML = "New title";

// Modifying textContent
element1.textContent = "New content";

// Modifying attributes
titleElement.setAttribute("data-info", "my-title");

// Modifying style
element1.style.color = "blue";

// Modifying CSS classes
element1.classList.add("highlight"); // Add class
element1.classList.remove("content"); // Remove class
element1.classList.toggle("active"); // Toggle class

Creating and Inserting Elements

JavaScript provides methods to create new elements:

document.createElement(): Creates a new HTML element.
document.createTextNode(): Creates a new text node.
appendChild(): Adds a node as a child to another node.
insertBefore(): Inserts a node before a specific child node.
removeChild(): Removes a child node from another node.

// Creating element
let newParagraph = document.createElement("p");

// Creating text node
let textNode = document.createTextNode("This is a new paragraph.");

// Appending the text node to paragraph element
newParagraph.appendChild(textNode);

// Appending the element to the body
document.body.appendChild(newParagraph);

// Inserting before another element
document.body.insertBefore(newParagraph, element1);

// Removing an element from document
document.body.removeChild(element1);

Handling Events

JavaScript can respond to events triggered by user interactions (e.g., mouse clicks, keyboard input, page loading):

addEventListener(): Attach an event listener to an element.
Event handlers (e.g., onclick, onload, onmouseover, onkeyup).

// Using addEventListener
let button = document.querySelector("button");

function handleClick() {
  alert("Button clicked");
}
button.addEventListener("click", handleClick);

// Using event handlers
// <button onclick="handleClick()">Click me</button> // Handle in HTML

Key Takeaways for Students

The DOM is a tree-like structure of objects that represents an HTML document.
Use methods like getElementById(), querySelector(), etc., to select elements.
Modify element properties using innerHTML, textContent, setAttribute(), style, and classList.
Create new elements using document.createElement() and insert them into the DOM using appendChild().
Use addEventListener() to handle events and make web pages interactive.

4. Asynchronous JavaScript

Asynchronous JavaScript allows you to perform operations without blocking the main thread, ensuring smooth and responsive user interfaces. This is especially important for tasks that take time, such as fetching data from servers or handling timers.

Synchronous vs Asynchronous Code

Synchronous code executes line by line, one after the other. Each line waits for the previous one to complete.
Asynchronous code allows operations to run in the background without blocking other operations. When an asynchronous operation is completed, a callback, a promise, or async function is used to handle the result.

// Synchronous code
console.log("First");
console.log("Second");
console.log("Third"); // Output: First, Second, Third

// Asynchronous code (using setTimeout)
console.log("First");
setTimeout(function () {
  console.log("Second");
}, 1000); // Waits 1 second
console.log("Third"); // Output: First, Third, Second (out of order)

Callbacks

A callback is a function passed as an argument to another function and executed when the operation is complete. Callbacks can lead to "callback hell," which is complex to maintain when nested.

function fetchData(callback) {
  setTimeout(function () {
    const data = { message: "Data fetched" };
    callback(data);
  }, 1000);
}

function processData(data) {
  console.log("Processing data:", data.message);
}
fetchData(processData); // Output: Processing data: Data fetched (after 1 second)

Promises

Promises are objects representing the eventual completion (or failure) of an asynchronous operation and help to make asynchronous code more readable and maintainable. A promise has three states: pending, fulfilled (resolved), or rejected.

function fetchDataPromise() {
  return new Promise(function (resolve, reject) {
    setTimeout(function () {
      const data = { message: "Data fetched with promise" };
      resolve(data);
    }, 1000);
  });
}

fetchDataPromise()
  .then(function (data) {
    console.log("Promise resolved:", data.message); // Output: Promise resolved: Data fetched with promise (after 1 second)
  })
  .catch(function (error) {
    console.error("Promise rejected:", error);
  });

`async/await`

The async/await syntax simplifies working with promises, making asynchronous code look more synchronous. An async function always returns a promise, and await pauses the execution until the promise resolves.

async function fetchDataAsync() {
  try {
    const data = await fetchDataPromise();
    console.log("Async data:", data.message);
  } catch (error) {
    console.error("Async error:", error);
  }
}
fetchDataAsync(); // Output: Async data: Data fetched with promise (after 1 second)

Event Loop

JavaScript runs on a single thread, and it uses an event loop to handle asynchronous operations. The event loop constantly checks the call stack and the callback queue and moves tasks to the call stack when the stack is available.

Key Takeaways for Students

Asynchronous code executes non-blocking, ensuring smooth UI responsiveness.
Use callbacks to handle the result of asynchronous operations.
Promises help in managing async operations, and avoid "callback hell".
async/await makes asynchronous code more readable and manageable.
The event loop handles asynchronous operations and call stack.

5. JSON and AJAX

JSON (JavaScript Object Notation) is a lightweight data-interchange format that is easy for humans to read and write, and easy for machines to parse and generate. AJAX (Asynchronous JavaScript and XML) is a technique for making HTTP requests to a server from a web page without reloading the entire page. AJAX is used for transferring data like JSON.

JSON

JSON is a format for structured data. It consists of key-value pairs similar to JavaScript objects but uses a specific string format. JSON data types include: strings, numbers, boolean values, null, objects, and arrays.

{
  "name": "John Doe",
  "age": 30,
  "isStudent": false,
  "address": {
    "city": "New York",
    "country": "USA"
  },
  "courses": ["math", "science"]
}

`JSON.stringify()` and `JSON.parse()`

JSON provides methods to:

JSON.stringify(): Convert a JavaScript object to a JSON string.
JSON.parse(): Convert a JSON string to a JavaScript object.

let person = {
  name: "John Doe",
  age: 30,
  occupation: "Developer",
};
let jsonString = JSON.stringify(person);
console.log(jsonString); // Output: {"name":"John Doe","age":30,"occupation":"Developer"} (as a string)
let parsedPerson = JSON.parse(jsonString);
console.log(parsedPerson); // Output: {name: 'John Doe', age: 30, occupation: 'Developer'} (as a Javascript Object)

AJAX

AJAX uses XMLHttpRequest or fetch to make asynchronous HTTP requests to a server and then updates the UI based on the server response.

// Using XMLHttpRequest (older)
function fetchData(url) {
  const xhr = new XMLHttpRequest();
  xhr.open("GET", url);
  xhr.onload = function () {
    if (xhr.status === 200) {
      const data = JSON.parse(xhr.responseText);
      console.log(data);
    } else {
      console.error("Request failed with status:", xhr.status);
    }
  };
  xhr.onerror = function () {
    console.log("Error in request");
  };
  xhr.send();
}
fetchData("https://jsonplaceholder.typicode.com/todos/1");

Using Fetch API (Modern)

The fetch API is a modern way to make HTTP requests. It is a promise-based API, making it easier to work with asynchronous operations.

function fetchData(url) {
  fetch(url)
    .then(function (response) {
      if (!response.ok) {
        throw new Error(`HTTP error! status: ${response.status}`);
      }
      return response.json(); // Parse response to json
    })
    .then(function (data) {
      console.log(data);
    })
    .catch(function (error) {
      console.error("Error:", error);
    });
}
fetchData("https://jsonplaceholder.typicode.com/todos/1");

Using Fetch API with async/await

async function fetchDataAsync(url) {
  try {
    const response = await fetch(url);
    if (!response.ok) {
      throw new Error(`HTTP error! status: ${response.status}`);
    }
    const data = await response.json();
    console.log(data);
  } catch (error) {
    console.error("Error", error);
  }
}
fetchDataAsync("https://jsonplaceholder.typicode.com/todos/1");

Key Takeaways for Students

JSON is a standard format for structured data exchange.
JSON.stringify() converts a JavaScript object to a JSON string.
JSON.parse() converts a JSON string to a JavaScript object.
AJAX enables asynchronous communication between web pages and servers.
Use fetch or XMLHttpRequest to make HTTP requests.
Handle asynchronous HTTP requests using promises and async/await.

6. ES6 and Modern JavaScript

ES6 (ECMAScript 2015) and beyond introduce many new features and improvements to JavaScript. They enhance code readability, make it easier to write complex applications, and help to stay up-to-date with modern web development practices.

`let` and `const`

let and const are block-scoped variable declarations, offering improvements over var. let allows reassignment; const doesn't.

let count = 10;
count = 20; // Allowed
const PI = 3.14;
// PI = 3.1415; // Error: Assignment to constant variable

Arrow Functions

Arrow functions provide a shorter syntax for writing function expressions. They also have a different way of handling the this keyword.

// Regular function
// function add(a, b) {
// return a + b;
// }

// Arrow function
const add = (a, b) => a + b;
const multiply = (a, b) => {
  return a * b;
};
// Arrow function with no arguments
const logMessage = () => console.log("Hello");
console.log(add(5, 3));
logMessage();

Template Literals

Template literals use backticks (`) and allow string interpolation using ${expression}.

let name = "John";
let age = 30;
let message = `Hello, my name is ${name} and I am ${age} years old.`;
console.log(message);

Destructuring

Destructuring allows you to unpack values from arrays and objects into distinct variables.

// Array destructuring
let colors = ["red", "green", "blue"];
let [first, second] = colors;
console.log(first); // Output: red

// Object destructuring
let person = {
  name: "Alice",
  age: 25,
};
let { name: fullName, age: years } = person;
console.log(fullName); // Output: Alice

Spread and Rest Operators

Spread operator (...) allows arrays and objects to be expanded.
Rest operator (...) collects parameters into an array.

// Spread operator
let arr1 = [1, 2, 3];
let arr2 = [...arr1, 4, 5]; // Expands arr1, and adds more values
console.log(arr2); // Output: [1, 2, 3, 4, 5]

// Rest operator
function sum(...numbers) {
  return numbers.reduce((total, num) => total + num, 0);
}
console.log(sum(1, 2, 3, 4)); // Output: 10

Classes

ES6 introduces class syntax for creating objects and managing inheritance.

class Person {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }
  greet() {
    return `Hello, I am ${this.name}.`;
  }
}
let person1 = new Person("Bob", 28);
console.log(person1.greet()); // Output: Hello, I am Bob.

Modules

Modules allow you to organize code into separate files and share variables, functions, and classes between files.

// Named exports
// export const PI = 3.14159;
// export function add(a, b) {return a + b};

// Named imports
// import { PI, add } from "./myModule.js";

// Default exports
// export default function sayHello(name) {console.log(`Hello ${name}`)}
// Default imports
// import sayHello from "./myModule.js";

Key Takeaways for Students

ES6 and modern JavaScript include new features that improve your code.
let and const provide better variable declarations.
Arrow functions offer concise syntax for functions.
Template literals allow for easy string interpolation.
Destructuring helps unpack values from arrays and objects.
Spread and rest operators enhance array and object manipulation.
Classes provide a mechanism for object-oriented programming.
Modules enable code organization and reusability.

7. JavaScript Libraries

JavaScript libraries provide pre-written code that can be used to perform common tasks, saving time and effort and enhancing code efficiency. Libraries improve development speed, and are used for frontend and backend projects.

Introduction to Libraries

Libraries consist of collections of reusable functions and objects.
They provide solutions for common programming tasks.
They can be used with script tag or with import statements.
Popular categories include UI libraries, utility libraries, and data visualization libraries.

UI Libraries (e.g., React, Angular, Vue.js)

Used to build user interfaces.
Provide reusable UI components, data binding, and state management.
Examples include:
- React: Library for building user interfaces using a component-based approach and virtual DOM.
- Angular: Framework for building complex applications with dependency injection, templates, and routing.
- Vue.js: Progressive framework for building single-page applications and user interfaces with templates and reactivity.

// Example: React component
function Greeting(props) {
  return <h1>Hello, {props.name}!</h1>;
}

Utility Libraries (e.g., Lodash, Underscore)

Provide helper functions for common tasks.
Include functions for array manipulation, object operations, string processing, etc.
Examples include:
- Lodash: Extensive utility library with hundreds of functions for data manipulation.
- Underscore: Lightweight utility library for functional programming in JavaScript.

// Example: Using Lodash
const _ = require("lodash");
console.log(
  _.map([1, 2, 3], function (num) {
    return num * 2;
  })
); // Output: [2, 4, 6]
console.log(_.uniq([4, 8, 4])); // Output: [ 4, 8 ]

Data Visualization Libraries (e.g., Chart.js, D3.js)

Used to create interactive charts and graphs.
Provide APIs for creating various types of charts, such as bar charts, line charts, pie charts, etc.
Examples include:
- Chart.js: Simple library for creating charts using HTML5 canvas.
- D3.js: Library for manipulating the DOM with data-driven approaches to create complex visualizations.

How to Use Libraries

Include via CDN (content delivery network): Add a <script> tag that links to the library's hosted file in the HTML file.

<script src="https://cdn.jsdelivr.net/npm/lodash@4.17.21/lodash.min.js"></script>

Download and use in project: Download the library's file and include it in the project. Link the library file via script tag or import statement.

import _ from "lodash";

Install via package manager: Install the library using npm or yarn, then import it using import or require.

npm install lodash

import _ from "lodash";

Key Takeaways for Students

JavaScript libraries help in development by providing reusable code.
Use UI libraries (e.g., React, Angular, Vue.js) to build dynamic user interfaces.
Use utility libraries (e.g., Lodash, Underscore) for common tasks.
Use data visualization libraries (e.g., Chart.js, D3.js) to create charts and graphs.
You can include libraries via CDN or local installations.
Explore a few libraries and focus on understanding how to use them.

Unit 7 Questions for Exam Preparation

Note > Refer to all old and model questions and solve them. This is crucial for exam preparation as these questions are directly aligned with the syllabus and have been tested in previous exams. Make sure to practice them thoroughly!

Scope and Closures

Explain the difference between global and local scope in JavaScript.
What is block scope, and how does it differ from function scope?
What is a closure in JavaScript? Provide an example.
How can closures be used to create private variables?
Explain how closures are used in callbacks?
What are some practical use cases for closures in web development?
Explain lexical scoping and how it relates to closures.
Differentiate between scope and context with examples. (Spring 2024, Q11)
What are IIFEs and how they are related to scopes?

Error Handling and Debugging

List and explain three types of errors in JavaScript.
What is the purpose of the try...catch statement?
How do you throw custom errors using the throw statement?
What is the purpose of the finally block in a try...catch...finally statement?
Describe three debugging techniques for JavaScript code.
What is a stack trace? How can it be helpful?
Explain different error object properties.
How do you manage different errors using try-catch block?

DOM Manipulation

What is the DOM?
How is the DOM tree-like structure?
List and describe four methods to select HTML elements in JavaScript.
What is the difference between innerHTML and textContent?
How do you set inline styles in JavaScript?
How to add and remove css classes using javascript.
How to create a new element in javascript.
How to add events using addEventListener.
What is an event handler? Explain different event handlers?
What is NodeList? Differentiate with HTMLCollection.

Asynchronous JavaScript

Explain the difference between synchronous and asynchronous code.
What is a callback function?
Explain what a promise is and how it works.
What are the three states of a promise?
What is the purpose of the async and await keywords?
How do async functions relate to promises?
What is the event loop and how it works?
What is callback hell, and how can you avoid it?
Write an example of how to perform some asynchronous task using callback.
Write an example of how to perform some asynchronous task using Promises and async/await keywords?

JSON and AJAX

What is JSON, and why is it used in web development?
Explain the difference between JSON.stringify() and JSON.parse().
What is AJAX?
How does AJAX help in web development?
Compare XMLHttpRequest and fetch API for making HTTP requests.
How is JSON used with AJAX?
What are the possible states of request while working with AJAX?
How do you get the status code for a HTTP request?
How do you manage different states of request using javascript?
Write an example to make a fetch call and handle response.

ES6 and Modern JavaScript

What are the advantages of using let and const over var?
How do arrow functions differ from regular functions?
What are template literals, and why are they useful?
Explain how destructuring works for arrays and objects.
What are spread and rest operators, and how can they be used?
How do classes work in JavaScript?
What are JavaScript modules?
Differentiate between named exports and default exports.
List the new feature of ES6 version of JavaScript. (Spring 2024, Q14a)
Briefly describe ES6. (Fall 2023, Q15)

JavaScript Libraries

What is a JavaScript library?
Name three common categories of JavaScript libraries and provide an example of each.
Give three examples of popular UI libraries, and list one advantage of each.
Give two examples of utility libraries, and list one advantage of each.
Give two examples of data visualization libraries, and list one advantage of each.
Describe three ways to include a JavaScript library in your project.
Explain some differences between libraries and frameworks in JavaScript?
What is the use of a CDN in Javascript?
What is package manager? How it works?
How to make use of different libraries in Javascript?

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JavaScript Basics and Advanced Concepts

JavaScript Fundamentals

Table of Contents

1. History of JavaScript

2. Introduction to JavaScript

3. Using JavaScript in HTML

4. JavaScript Output

5. JavaScript Comments

6. Variables in JavaScript

7. Data Types in JavaScript

8. Operators and Expressions

9. Control Flow and Conditionals

10. Loops

11. Functions

12. Arrays

13. Objects

Unit 6 Questions for Exam Preparation

Introduction to JavaScript

Using JavaScript in HTML

JavaScript Output

JavaScript Comments

Variables in JavaScript

Data Types in JavaScript

Operators and Expressions

Control Flow and Conditionals

Loops

Functions

Arrays

Objects

Unit 7: Advanced JavaScript Concepts

1. Scope and Closures

Scope

Global Scope

Local (Function) Scope

Block Scope

Closures

Uses of Closures

Key Takeaways for Students

2. Error Handling and Debugging

Types of Errors

try...catch Statement

Throwing Errors

Debugging Techniques

Error Object

Key Takeaways for Students

3. DOM Manipulation

Understanding the DOM

Selecting Elements

Modifying Elements

Creating and Inserting Elements

Handling Events

Key Takeaways for Students

4. Asynchronous JavaScript

Synchronous vs Asynchronous Code

Callbacks

Promises

async/await

Event Loop

Key Takeaways for Students

5. JSON and AJAX

JSON

JSON.stringify() and JSON.parse()

AJAX

Using Fetch API (Modern)

Using Fetch API with async/await

Key Takeaways for Students

6. ES6 and Modern JavaScript

let and const

Arrow Functions

Template Literals

Destructuring

Spread and Rest Operators

Classes

Modules

Key Takeaways for Students

`try...catch` Statement

`async/await`

`JSON.stringify()` and `JSON.parse()`

`let` and `const`

Packages