Conclusion
TypeScript is a popular choice for type checking your JavaScript code. There are other options to consider, like Flow (Facebook), but the TypeScript community is much larger and active. Along with the support of Microsoft, TypeScript has proven to be a viable technology to add to your current stack with support from the three mainstream frameworks.
With this technology, your code is easier to maintain, easier to refactor, easier to work with larger groups, and will help prevent errors in your code. Since the browser cannot read TypeScript, the pre-packaged compiler must be running to convert to .ts files to .js files (ES6 or later, ES5 or earlier).