What is TypeScript?

TypeScript is actually two distinct but related technologies – a language and a compiler:

• The language is a feature-rich, statically typed programming language that adds true object-oriented capabilities to JavaScript.
• The compiler converts TypeScript code into native JavaScript, but also provides the programmer with assistance in writing code with fewer errors.

TypeScript enables the developer to design software that's of a higher quality. The combination of the language and the compiler enhances the developer's capabilities. By using TypeScript, a developer can write code that is easier to understand and refactor and contains fewer bugs. Additionally, it adds discipline to the development workflow by forcing errors to be fixed while still in development.

TypeScript is a development-time technology. There is no runtime component and no TypeScript code ever runs on any machine. Instead, the TypeScript compiler converts TypeScript into JavaScript and that code is then deployed and run on browsers or servers. It's possible that Microsoft considered developing a runtime for TypeScript. However, unlike the operating system market, Microsoft does not control the ECMAScript standards body (the group that decides what will be in each version of JavaScript). So, getting buy-in from that group would have been difficult and time-consuming. Instead, Microsoft decided to create a tool that enhances a JavaScript developer's productivity and code quality.

So then, if TypeScript has no runtime, how do developers get running code? TypeScript uses a process called transpilation. Transpilation is a method where code from one language is "compiled" or converted into another language. What this means is that all TypeScript code ultimately is converted into JavaScript code before it is finally deployed and run.

In this section, we've learned what TypeScript is and how it works. In the next section, we'll learn about why these features are necessary for building large, complex applications.