VeilObjects

The JS/TS implementation of Veil objects approach from EO oriented programming

Notice that the package is under active development currently.

Objectives

See original paper which this package idea is based upon - https://www.yegor256.com/2020/05/19/veil-objects.html

The objective is to use the EO oriented programming so callsed: "Veil objects" approach in JS/TS

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Contributing

See all you need here: https://gadzhievislam.org/Programming/Contributing

Issues

You're welcome to submit any issues related to existing issues tags, and start to work on existing.

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Usage

The veil object wraps a target object with provided presets object and when trying to access the provided presets methods on the veil object 0 it passes them throuhg, until the veil object is pierced, meaning the use methods not listed in the provided preset object.

See the example below in TypeScript:

// Create a Project class with dynamic methods

type TDBFetcher = (field: string, id: number) => string;

class Project {
  constructor(
    private readonly dataFetcher: TDBFetcher,
    private readonly id: number
  ) {
    this.dataFetcher = dataFetcher;
    this.id = id;
  }

  name(): string {
    return this.dataFetcher("name", this.id);
  }

  author(): string {
    return this.dataFetcher("author", this.id);
  }

  description(): string {
    return this.dataFetcher("description", this.id);
  }
};

Now let's try to use our Veil object:

JavaScript

const veiledProject = new Veil(
  new Project(fetchData, 1),
  { name: 'project-1', author: 'Alex' },
);

TypeScript

const veiledProject = new Veil(
  new Project(fetchData, 1),
  { name: 'project-1', author: 'Alex' },
) as unknown as Project;

// As you might've witnessed a nuance for using with TypeScript:
// The only way to infer the target object types from the dynamic nature of Veil class for TypeScript
// is to use type casting with - `as unkown as <targetType>`.
//
// That's why it's strongly recommended to either:
// - Use the Veil only in JS code
// - Find some workarounds for TS

Tests:

// Asserting
// Call methods on the veiled object
console.log( veiledProject.name() ); // Outputs: "project-1" (preset value)
console.log( veiledProject.author() ); // Outputs: "Alex" (preset value)

// Accessing a non-preset method pierces the veil
console.log( veiledProject.description() ); // Pierces the veil and fetches from `project`

// Now fetches via target object native method: `project.name()`, no longer uses preset
// Outputs: "project.name()", wher `project` is `new Project()` from the Veil target
console.log( veiledProject.name() );