give a button a onclick js 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

document.getElementById("Save").onclick = function ()
    {
     alert("hello");
     //validation code to see State field is mandatory.  
    }