chartjs/Chart.js — reverse-engineered prompt

Build me a simple but flexible JavaScript charting library for the browser that draws charts with the HTML5 canvas element. I want someone to be able to drop it into a web page, pass in data plus a configuration object, and get clean responsive charts with very little setup. It should handle common chart needs, support labels, axes, legends, tooltips, colors, animation, and let people customize behavior and styling without the API feeling confusing.

Please make it feel polished for both designers and developers, with sensible defaults, clear documentation, a few working examples, and tests so it is dependable. I also want it to be easy to maintain and easy to extend later. If you need to, look up the current docs and browser best practices online while building it. Keep the overall experience lightweight, modern, and focused on simple HTML5 charts that are pleasant to use.