Answers for "how to on click on javascript"

javascript onclick button

var button = document.querySelector('button');
button.onclick = function() {
  //do stuff
}

javascript onclick

var myElem = document.getElementByID('ElemID');
myElem.onclick = function() {
	//do stuff
}

javascript click event

<button onclick="myFunction()">Click me</button>

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

<script>
function myFunction() {
  document.getElementById("demo").innerHTML = "Hello World";
}
</script>