Tryit Editor v2.9

Edit This Code:
<!DOCTYPE html>
<html>
<body>

<p>Click the button to join three strings into one new string.</p>

<button onclick="myFunction()">Try it</button>

<p id="demo"></p>

<script>
function myFunction() {
    var str1 = "Hello ";
    var str2 = "world!";
    var str3 = " Have a nice day!";
    var res = str1.concat(str2, str3);
    document.getElementById("demo").innerHTML = res;
}
</script>

</body>

</html>