Comment by JimDabell

jQuery in ~2008 was when it kinda took off, but jQuery was itself an outgrowth of work done before it on browser compatibility with JavaScript. In particular, events.

Internet Explorer didn’t support DOM events, so addEventListener wasn’t cross-browser compatible. A lot of people put work in to come up with an addEvent that worked consistently cross-browser.

The DOMContentLoaded event didn’t exist, only the load event. The load event wasn’t really suitable for setting up things like event handlers because it would wait until all external resources like images had been loaded too, which was a significant delay during which time the user could be interacting with the page. Getting JavaScript to run consistently after the DOM was available, but without waiting for images was a bit tricky.

These kinds of things were iterated on in a series of blog posts from several different web developers. One blogger would publish one solution, people would find shortcomings with it, then another blogger would publish a version that fixed some things, and so on.

This is an example of the kind of thing that was happening, and you’ll note that it refers to work on this going back to 2001:

https://robertnyman.com/2006/08/30/event-handling-in-javascr...

When jQuery came along, it was really trying to achieve two things: firstly, incorporating things like this to help browser compatibility; and second, to provide a “fluent” API where you could chain API calls together.