How to add a typescript definition file to a npm package?

Question

Is there a way to add typescript definitions (.d.ts files) to a pure javascript project directly (e.g. in package.json). I can't find any documentation on that.

Answer 1

There is a page in the TypeScript Handbook on adding typings to an NPM Package. I'll copy and paste here:

Typings for NPM Packages

The TypeScript compiler resolves Node module names by following the Node.js module resolution algorithm. TypeScript can also load typings that are bundled with npm packages. The compiler will try to discover typings for module "foo" using the following set of rules:

Try to load the package.json file located in the appropriate package folder (node_modules/foo/). If present,read the path to the typings file described in the "typings" field. For example, in the following package.json, the compiler will resolve the typings at node_modules/foo/lib/foo.d.ts

{
    "name": "foo",
    "author": "Vandelay Industries",
    "version": "1.0.0",
    "main": "./lib/foo.js",
    "typings": "./lib/foo.d.ts"
}

Try to load a file named index.d.ts located in the package folder (node_modules/foo/) - this file should contain typings for the package.

The precise algorithm for module resolution can be found here.

Your definition files should

• be.d.ts files

• be written as external modules
• not contain triple-slash references

The rationale is that typings should not bring new compilable items to the set of compiled files; otherwise actual implementation files in the package can be overwritten during compilation. Additionally, loading typings should not pollute global scope by bringing potentially conflicting entries from different version of the same library.

Answer 2

Visual Studio 2015 will not recognize the definition file unless you use the types property in package.json
https://www.typescriptlang.org/docs/handbook/declaration-files/publishing.html

{
   "name": "awesome",
   "author": "Vandelay Industries",
   "version": "1.0.0",
   "main": "./lib/main.js",
   "types": "./lib/main.d.ts"
}

*You will have to use the three slashes include reference path in your ts files.
/// <reference path="../node_modules/../lib/main.d.ts" />

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For anyone else landing here & wanting to link types to their npm package, a handy tutorial that might help!