TypeScript is a programming language developed by Microsoft that adds optional static typing to JavaScript. Every valid JavaScript program is also a valid TypeScript program; TypeScript layers a type system on top, then compiles down to ordinary JavaScript that runs in any browser or runtime.
Microsoft first released TypeScript in October 2012. In the official announcement of the 1.0 release, the team wrote, “When we introduced TypeScript to the world with our first release, TypeScript 0.8 in October 2012, we couldn’t have imagined how the community would take shape.” That 1.0 milestone was announced in April 2014, about eighteen months after the language’s debut.
The language was designed by Anders Hejlsberg, who had earlier created Turbo Pascal and led the design of C# at Microsoft. The motivating problem was scale: as JavaScript applications grew into hundreds of thousands of lines, the absence of compile-time type checking made large codebases fragile and hard to refactor. TypeScript’s types catch many errors before the code ever runs and power editor features like reliable autocompletion and safe renaming.
Because TypeScript output is plain JavaScript, it slots into existing toolchains without requiring a new runtime. Over time it became one of the most widely adopted ways to write large-scale JavaScript, especially for the component-based, single-page applications that dominate modern web development.