TypeScript is a superset of JavaScript with optional static typing. The DefinitelyTyped project contains type definitions for major JavaScript libraries contributed by the community. You can use these definitions and TypeScript’s compiler to check your code for errors, just by adding references.

We have a large AngularJS project. I’d like to type-check all our code and maybe find a few bugs.

Install TypeScript

Clone DefinitelyTyped to references

The DefinitelyTyped project provides type definitions for AngularJS, Jasmine and about 100 other common JavaScript libraries.

To keep it simple, I’m just going to clone the whole lot into my project, where I can reference anything I need.

Rename All .js Files To .ts

By renaming all our files, we let tsc and other tools know the code should be treated as TypeScript.

Let’s give our unix skills a workout and do this with a find one-liner:

Create References Includes For The Project

TypeScript code needs to be annotated with comments to link to the type definitions we downloaded from DefinitelyTyped. E.g. for a Jasmine spec which tests an Angular controller, we might need the following block at the top of the file:

You’ll need a reference for each library you’re using. To simplify things, let’s create a couple of reference files which define the shared references for our module definitions and test specs and include those in our code.

Note that test.ts references module.ts.

Add References To All .ts Files

Now, let’s add the references to every TypeScript file with a couple more find one-liners (requires GNU sed, if you’re on OS X, install with brew install gnu-sed --default-names).

Phew!

The path attribute needs to be right. Luckily, all of the code in our project is 5 levels deep in the directory structure. If your code doesn’t have such a regular structure, you’ll need to do something more clever.

Compile Everything With tsc

Finally, let’s run everything through the TypeScript compiler and see the issues we have to resolve:

Adding Definitions For Missing Modules

Adding type definitions for your own modules or 3rd-party modules missing from DefinitelyTyped is straightforward. A few examples: