start js function when clicked html code example
Example 1: how to call a function with a button in javascript
<script>
function myFunction()
{
document.write("<h1>HELLO</h1>")
}
</script>
<button onclick="myFunction()">Click</button>
Example 2: javascript onclick button
var button = document.querySelector('button');
button.onclick = function() {
//do stuff
}