Try this:
<!doctype html>
<head>
<title>Javascript with HTML</title>
<script>
/ JS in the head section /
function doSomething() {
document.getElementById("heading").textContent = "New heading";
}
</script>
</head>
<body>
<h1 id="heading">Some Page Heading</h1>
<button onclick="doSomething()">Click me!</button>
</body>
</html>
You have to add doSomething() function in the onclick attribute.
