encryption js

<!DOCTYPE html>
<html>
<body>
<script>
function enc() {
var s = document.getElementById("text").value;
var t = "";
for(let i = 0; i < s.length; i++)
 {
 t += DO(s[i]);
 }
 document.getElementById("out").innerHTML = t;
}

function DO(x){
switch(x){
case "a":
return "s";
break;
case "b":
return "x";
break;
}
}
</script>

<input type="text" id="text">
<button onclick="enc()">Click</button>
<h1 id="out"></h1>


</body>
</html>