javascript onclick button

document.getElementById('button').onclick = function() {
   alert("button was clicked");
};

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

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

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

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

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

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

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

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

 <input type="checkbox" id="myCheck" onmouseover="myFunction()" onclick="alert('clicked')">

 function myFunction() {
  document.getElementById("myCheck").click(); // Click on the checkbox
}

<button onClick="script">