JSFiddle - React, Tailwind, and code Playground

JavaScript

var input = "javascript is awesome leet";
var output = "";
for (let i = 0; i<input.length; i++) {
  let symbol = input[i]
  switch (symbol) {
    case 'a': output += '4'; break;
    case 'e': output += '3'; break;
    case 'i': output += '1'; break;
    case 'o': output += '0'; break;
    case 't': output += '7'; break;
    default: output += symbol;
  }
}
console.log(output)