Add a method inside the prototype of Number or String

addNewMethodInPrototype.js

const aNumber = 13254
const aString = 'aa'

// We add a method in the prototype of Number and String
Number.prototype.sort = function() {
  return Number(this.toString().split('').sort((a,b)=>a-b).join(''))
}
String.prototype.capitalize = function() {
  return this.charAt(0).toUpperCase() + this.slice(1)
}

console.log(aNumber.sort()) // Expected: 12345
console.log(aString.capitalize()) // Expected: 'Aa'