Tryit Editor v2.9

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

<p>x = 10 and y = 5, calculate x -= y, and display x:</p>
<button onclick="myFunction()">Try it</button>

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

<script>
function myFunction() {
    var x = 10;
    var y = 5;
    x -= y;
    document.getElementById("demo").innerHTML = x;
}
</script>

</body>
</html>