https://frontendmasters.com/courses/intermediate-react-v2/typescript-introduction/

Why TypeScript

there's more on TypeScript on frontendmasters.

example:

  var x = 5

x.toUpperCase()

TypeScript will tell you before running the code that this will produce an error.

It adds great autocompletion and code intellisense features, eg. type signature etc.

It gives interactive documentation.

The TypeScript and VSCode team are just across the hall at Microsoft.