Read "You Don't know JS" in your browser: https://codesandbox.io/s/m55nl9
"You Don't know JS" is a series of 6 books written by Kyle Simpson (getify) that teach you JavaScript.
I made this webpage so you can more easily read the markdown files that are publicly available under https://github.com/getify/You-Dont-Know-JS
Consider buying a copy of the 2nd edition since Kyle Simpson is publishing the books for free under a Creative Commons 4.0 license.
I also started a version with svelte: https://github.com/TobiObeck/ydkjs-reader