<!DOCTYPE html>
<html>
<body>
<p>Click the button to decode a base-64 encoded string.</p>
<button onclick="myFunction()">Try it</button>
<p><strong>Note:</strong> The atob() method is not supported in IE9 and earlier.</p>
<p id="demo"></p>
<script>
function myFunction() {
var str = "Hello World!";
var enc = window.btoa(str);
var dec = window.atob(enc);
var res = "Encoded String: " + enc + "<br>" + "Decoded String: " + dec;
document.getElementById("demo").innerHTML = res;
}
</script>
</body>
</html>