About this project

33-js-concepts is an open-source repository created by Leonardo Maldonado that curates foundational and advanced JavaScript topics for developers. It was highlighted by GitHub as one of the top open source projects of 2018. The project is available as a GitHub repository and as a full reading guide at 33jsconcepts.com. The main guide is organized around 33 core concepts, grouped into thematic sections: fundamentals, functions and execution, web platform APIs, object-oriented JavaScript, asynchronous programming, functional programming, and advanced topics. Each concept page typically includes a plain-English explanation, practical code examples, and links to recommended resources. Beyond the original 33 concepts, the repository has been expanded with an "Extended Concepts" section covering language mechanics, type system details, object property behavior, memory and performance, modern syntax and operators, browser storage, browser events, observer APIs, and data handling. Because the material is community-driven, the project welcomes contributions and has been translated into more than 40 languages. The license is MIT, so the guide and its examples can be freely reused with attribution.