In mid-2017, Lyft decided to introduce a type system to its large JavaScript code base. After assessing the options, they decided to move forward with TypeScript, emphasizing its popularity both among Lyft engineers as well as among the developer community as a whole.

Since adopting TypeScript, they team has implemented TSLint for linting all TypeScript projects, and have created many TypeScript-only project, like a custom React JavaScript-to-TypeScript converter and an integration with their internal CSS library.