var string = "Leet speak";
		var outputString = "";
		var letters = {
			a: "4",
			e: "3",
			o: "0",
			s: "5",
			t: "7",
			z: "2"
			};
		for (var i =0; i < string.length; i++){
			if (letters[i]){
				outputString = string.replace(letters[i]);
			}
		}
		console.log(outputString);