Chai is a popular assertion library for Node.js and browsers, facilitating behavior-driven development (BDD) and test-driven development (TDD). Offering a flexible syntax with expect, should, and assert interfaces, Chai simplifies writing readable and maintainable tests. Its extensive plugin ecosystem enables extending its functionality with custom assertions, seamlessly integrating into various testing frameworks, making Chai a versatile choice for robust JavaScript testing.
Chai's release frequency peaked in 2012, with several months exceeding 10 versions. Releases slowed significantly after 2017, with many months seeing no new versions. There was a small resurgence of releases in 2021, 2023, 2024 and August 2025, including major version updates.
Chai's npm package downloads show a general upward trend from March 2024 to August 2025. A significant surge occurred in June and July 2025, reaching over 107 million downloads. September 2025 data is partial, showing 16.8 million downloads so far, making trend analysis difficult.
