To invoke a JavaScript function as a function, call it like a normal custom JavaScript function.
Example
You can try to run the following code to call a JavaScript function as a function −
<html>
<head>
<script>
function Display()
{
document.write ("Hello World!");
}
</script>
</head>
<body>
<p>Click the following button to call the function</p>
<form>
<input type = "button" onclick = "Display()" value = "Display">
</form>
</body>
</html>