JSFiddle - React, Tailwind, and code Playground

JavaScript

var leet = {
    h: 1,
    e: 2,
    r: 3,
    o: 4,
    l: 5
};

var s = "hello";
var fin = "";

for (var i in s) {
    if (leet.hasOwnProperty(s[i])) {
        fin += leet[s[i]];
    } else {
        fin += i
    }
}
alert(fin);