What methods does the TypeScript compiler use to locate npm packages containing types?

When configuring the typescript compiler, you can utilize the tsconfig.json file. This will also give you access to options for finding type definition files using the typeRoots key.

By default:

All visible "@types" packages are automatically included in your compilation process. this includes packages found in node_modules/@types in any parent folder such as ./node_modules/@types/, ../node_modules/@types/, etc.

If a specific typeRoots is specified, only packages under that root will be included.

Some packages provide their type definitions in a separate @types/<package-name> package, like Jquery. On the other hand, there are packages like Firebase which come with bundled type definitions.

It's interesting how the typescript compiler can recognize Firebase definitions without needing to adjust the typeRoots setting. These definitions aren't located in @types directory and shouldn't be picked up by default logic.

typescriptnpmtypescript-definitions

Answer №1

When it comes to providing types for users in the TypeScript publishing docs, there are two main approaches: https://www.typescriptlang.org/docs/handbook/declaration-files/publishing.html

  1. Include types with your npm package,
  2. Publish to the @types organization on npm.

For larger libraries like Firebase, they have their own set of types available at packages/firebase/package.json#L58 or packages/database/package.json#L68.

Typescripts reads these referenced files under the "typings" property of all installed packages that are used in your code being compiled.

The distinction between using typeRoots and a standard import 'firebase' is:

  1. If types are provided in typeRoot, they will always be automatically included in the compilation process. This is particularly useful for libraries that modify the global context, such as jQuery, node, etc., which offer global functions that might otherwise be challenging to detect.

  2. You can explicitly import them by specifying import {Foo} from 'bar'. If the 'bar' package includes a typing property in its package.json, Typescript will recognize it alongside those in typeRoots.

The documentation elaborates on this:

It's important to note that automatic inclusion is primarily relevant when dealing with files containing global declarations (as opposed to module-declared files). In the case of an "import 'foo'" statement, for instance, TypeScript may still search through node_modules & node_modules/@types directories to locate the foo package.

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