I still remember the day I discovered Dan Steinman's Dynamic Duo Javascript library. It allowed me to do effects that I thought were reserved only for flash or java embedded applets. That was in late 1999, probably while I was struggeling to make a crappy script copied from dynamicdrive.com work in Netscape 4. Tell me about eras!!
The "Before Era" mentioned in the article can probably be subdivided further - it casually mentions that back then, "the most common thing you would do was include jQuery, throw together some scripts for a few UI widgets, and call it a day". However that was only possible after jQuery was released in 2006. Before that were the real "dark ages" of JS development, with primitive libraries, even more primitive dev tools in the browser (Firebug was also only released in 2006, and Chrome was the first browser to have integrated dev tools in 2008) and stuff like "be careful with console.log in IE, because it will crash your script unless the console is actually visible".
jQuery didn't even incept that, prototype.js did. Prototype is probably the first real jS library that moved the language (along with Dojo, Mochi, etc) from scriplets ("DHTML") to actual UI interactivity. That + XMLHttpRequest ("Ajax") were the direct progenitors to jQuery, which was used to bootstrap or complement all of the early "frameworks".
I came here looking for this comment; it seems prototype is always forgotten about as part of the "before frameworks" discussion. I remember bringing up using prototype to my coworkers in 2006/2007 (the director was a stickler for having clickable buttons that had a specific width on the left and right of the text, so I proposed using prototype to set that automatically). I recall my coworkers being mostly confounded by it and how to use it.
Didn’t Opera and Safari have Dev tools before Chrome? I remember when Chrome got released they had to replace WebKit’s debugger with their own thing, because that’s the only thing they could do to support V8.
IE6 actually did have dev tools, you just had to install them as a separate package from Microsoft. They simply weren't that useful though.