as soon as page loads select tag will call the functions code example
Example 1: how to call a function as soon as a page loads javascript
<body onload="yourFunction()"> </body>
Example 2: call a function when page is loaded
<script src="js/jquery-1.11.0.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(document).ready(function () {
yourFunction();
});
function yourFunction(){
//some code
}
</script>