Will Script Loaded With Async Attribute Delay Onload Event?

I have a page with a script tag in HEAD section: As it contains async attribute it loads asynchronou

Solution 1:

Yes, as you suggest, it will delay the window.onload event.

Your first script, somescript.js adds a child script element to the page, before the page has finished loading (e.g. before window.onload has fired), and the page now has to download and execute the src of that newly appended script element before it can fire an onload event.

If you didn't want it to delay the onload event, you could make an AJAX request to get the contents of otherscript.js and simply eval it so it executes in the global context (effectively the same as specifying it via a script tag, but without delaying the onload event).