how to register button click html in javascript code example

Example 1: javascript onclick button

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

Example 2: button click function in js

<script>
  $(document).ready(function(){
    $('#MyButton').click(function(){
       CapacityChart();
    });
  });
</script>

<input type="button" value="Capacity Chart" id="MyButton" >