I also had my own js library (BellaJS) to handle the regular tasks by my way, so I can say that is the great way to improve JS coding skill.
Here are some experiences on what you should do next:
- Add support AMD/UMD so you can learn RequireJS, SystemJS, ES6 module, etc.
- Use jsPerf to compare the performance between your solution with the alternatives, so you can learn how to benmark and improve performance.
- Write unit test script so you can learn Jasmine, Jest, Mocha, etc.
- Travis or CircleCI integration will teach you how to automate some tasks in deployment process, that's a necessary step to make your lib can be used in production.
- Handle virtual DOM, publish to NPMJS.org
Just my two cents.