“Don't reinvent the wheel, unless you plan on learning more about wheels.”

The quote is by Jeff Atwood (aka @codinghorror).

What do you think about it? Did you ever try to build something that already exists, just out of curiosity, or to understand it better? How did it go?

I've recently written a Promise polyfill. I didn’t need it, it was not an urgent task, I didn’t have timelines, I didn’t have requirements about performance, weight, or anything else… it was a really fun, and instructive experience. These days I'm publishing on youtube a video series of myself, live-coding it. This is the first video https://www.youtube.com/watch?v=E_p-PVNqhZE, Any thoughts?