Microsoft first released TypeScript publicly in 2012 as a typed superset of JavaScript.
Anders Hejlsberg and other Microsoft engineers developed TypeScript to support large JavaScript applications with features such as static typing, classes, interfaces, and generics. TypeScript source code is compiled, or transpiled, into JavaScript that can run in web browsers and other JavaScript environments.
Because TypeScript is designed to be compatible with JavaScript, existing JavaScript code can generally be incorporated into TypeScript projects. Its type system is primarily checked during development and compilation rather than directly by the browser at runtime.
TypeScript is different from Dart, which Google developed as a separate language, and CoffeeScript, which uses a different syntax that compiles to JavaScript. Its file extension is commonly .ts, while JSX-containing files often use .tsx.