mini.js

const form=document.getElementById("form"),username=document.getElementById("username"),email=document.getElementById("email");function checkInputs(){const e=username.value.trim(),r=email.value.trim();""===e?setErrorFor(username,"Introduce tu nombre"):setSuccessFor(username),""===r?setErrorFor(email,"Email no puede ir en blanco"):isEmail(r)?setSuccessFor(email):setErrorFor(email,"Email no valido")}function setErrorFor(e,r){const t=e.parentElement,n=t.querySelector("small");t.className="form-control error",n.innerText=r}function setSuccessFor(e){e.parentElement.className="form-control success"}function isEmail(e){return/^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/.test(e)}form.addEventListener("submit",e=>{e.preventDefault(),checkInputs()});