what is defer in script tag code example

Example 1: async vs defer

Check this image for better understanding
//https://i.stack.imgur.com/wfL82.png

Async scripts are executed as soon as the script is loaded, so it doesn't guarantee the order of execution (a script you included at the end may execute before the first script file )
Defer scripts guarantees the order of execution in which they appear in the page.

Example 2: javascript defer

//A script that will not run until after the page has loaded

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

Example 3: javascript async script

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

Example 4: script deferred

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