This problem is not a simple problem of just creating and injecting the script file.

I want to optimize my website which loads script files of google ads.

Problem: When script files of google ads load parallelly with HTML files then page load speed drastically decreased.

Solution I came up with: I decided to load the script files of google ads after the webpage is 100% completely loaded (or even 100-200miliseconds after page 100% loaded)

Solutions I tried are as follows with details:

1. Created a function to load script file and used window.onload = loadGoogleSyndication(). But it actually loads the script before the complete loading of the HTML document. (i can observe it in the speed test of the site)

    function loadGoogleSyndication() {
      const googleSyndication = document.createElement('script');
      googleSyndication.type = 'text/javascript';
      googleSyndication.async = true;
      googleSyndication.src = 'https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js';
      const script = document.getElementsByTagName('script')[0];
      script.parentNode.insertBefore(googleSyndication, script);
    }
    window.onload = loadGoogleSyndication()
   

2. Secondly I used document.onload = loadGoogleSyndication(). But again it loads file before complete loading of page.

    window.onload = loadGoogleSyndication()

3. Same problem is with window.addEventlister("load", loadGoogleSyndication())

Only solution that worked: I use setTimeout property and loaded the file after 2.5 sec and then it worked. (2.5 sec can be 2sec also for fast internet connection)

This works 👇

window.addEventListener("load", function () {
  setTimeout(() => {
    loadGoogleSyndication();
  }, 2500);
}, true);

But is there any solution other than this where the script loads exactly after(or after 100 milliseconds) 100% HTML file loaded? Because using setTimeout property is throwing a knife in darkness we exactly don't know when the file HTML file load is completed.

One other solution could be to load file after window scrolled window.onscroll, but I don't want to use it.