Underscore.js / Lodash is probably the closest to what you are looking for. Here's why:
Lodash is a fork of Underscore, but on steroids. Both are great libraries! Learning them and digging deeper in their source code can greatly improve your Javascript knowledge.
Wanna take it one step further? No, problem - pick a random function from the library and rewrite it using your knowledge. After that compare your function with the original one - find the differences and similarities of both, try to understand why their approach is different than yours (if different) and refactor/optimize your function. You can even find a bug or piece of code, which can be further optimized - pull request that son of a btch. If accepted - congratulations, you just contributed to one of the coolest JavaScript libraries!