Dr. Axel Rauschmayer - Tackling TypeScript

While you are editing TypeScript code in an integrated development environment, you get warnings if you mistype names, call functions incorrectly, etc.

Consider the following two lines of code:

For the second line, we get this warning:

Another example:

This time, the error message for the last line is:

Documenting parameters of functions and methods is something that many people do, anyway:

Specifying the types via {number} and {string} is not required, but the descriptions in English mention them, too.

If we use TypeScripts notation to document types, we get the added benefit of this information being checked for consistency:

Whenever I migrate JavaScript code to TypeScript, Im noticing an interesting phenomenon: In order to find the appropriate types for parameters for a function or method, I have to check where it is invoked. That means that static types give me information locally that I otherwise have to look up elsewhere.

And I do indeed find it easier to understand TypeScript code bases than JavaScript code bases: TypeScript provides an additional layer of documentation.

This additional documentation also helps when working in teams because it is clearer how code is to be used and TypeScript often warns us if we are doing something wrong.