Pretty far, indeed.
A company I worked in had their entire frontend codebase written in in-house javascript. JQuery was the only external library linked but I never actually found where it was being used.
It was quite a lot of stuff: a full, feature-packed SOA client, something I would call an ORM even though it wasn't exactly it, a standard library of utilities and, more interestingly, a visual styling IDE for creating responsive websites based on tiling (like webflow), etc.
Yeah, there were no tests and massive refactoring could've gone a long way, besides changing a few idiosyncrasies (such as replacing SOA for full-featured REST among other stuff). But that they managed to build all that from scratch and it, mostly, worked I find a bit impressive.
The company eventually went under but the reason was not their technology.
All of that taught me to always think very carefully before deciding to use external libraries or full-featured frameworks, as I know that we can work without them and have worked like that already. I still reuse a lot, but I do so critically and will write my own code confidently if I feel that that will save me time and pain.