JSFiddle - React, Tailwind, and code Playground

JavaScript

var input = "javascript is awesome leet";
var replaceList = {
	'a': 4,
  'e': 3,
  'i': 1,
  'o': 0,
  't': 7,
}

var output = input.split('').map(s => replaceList[s] || s).join('')
console.log(output)