script tag into head code example

Example 1: how to add script in html head

<script src="script.js" defer></script>

<!--just add defer attribute so script will execute at last-->

Example 2: call js script in html

<script src="file1.js" type="text/javascript"></script> 
<script src="file2.js" type="text/javascript"></script>

Example 3: add javascript

function add(param1, param2) {
    return param1 + param2
}