make html button execute javascript code example

Example 1: run a function when a button has the onclick

<script>
function myFunction() {
  alert("ALERT THIS FUNCTION HAS RUNNED");
}
</script>
<button onclick="myFunction">click to run function</button>

Example 2: javascript onclick

// The element id (TheElementID) and var name (myElement) can be named anything.
var myElement = document.getElementByID('TheElementID');
myElement.onclick = function() {
	// Carry out a function here...
}