CODEWITHSUNDEEP
typescript
Nafiul Islam
Nafiul Islam

Reputation: 82590

Generating typescript declaration files from javascript

Say for example, you have a npm library, in my case mongoose, how would you go about generating d.ts files?

Upvotes: 77

Views: 89892

Answers (6)

Meligy
Meligy

Reputation: 36624

The question is a bit old, but for the sake of people coming from search engines like me, if you are looking for an automated tool, check out:

  • Microsoft/dts-gen

    The official starting point Microsoft uses when creating types. It's meant to be a starting point only though and I didn't get a lot of luck depending just on it

  • dtsmake

    This one looks very promising. It depends on Ternjs which some editors use to provide autocomplete for JS code. Check Ternjs out also for other tool names and comparisons with them.

Update (2021): It's a good idea to check npmtrends and compare dts-generator, dts-gen, dtsmake, npm-dts, and alternatives.

Upvotes: 38

Vytenis Urbonavičius
Vytenis Urbonavičius

Reputation: 11

You might want to have a look at "npm-dts" NPM package. It is a tool for generating single index.d.ts file for your NPM package so that it could be consumed by other TypeScript packages out of the box.

Upvotes: 1

Steve Brush
Steve Brush

Reputation: 3191

If you're attempting to use a third-party JavaScript library in your TypeScript file, you can create a custom (and nearly blank) declaration file anywhere in your project.

For example, if you wanted to import:

import * as fooLibrary from 'foo-lib';

You would create a new file named 'foo-lib.d.ts' with the following contents:

declare module 'foo-lib' {
  var fooLibrary: any;
  export = fooLibrary;
}

Upvotes: 9

Joost de Vries
Joost de Vries

Reputation: 640

For other people who find this post through google: there's a generator now by Microsoft itself: dts-gen.

Upvotes: 20

Fenton
Fenton

Reputation: 251232

JavaScript doesn't always contain enough type information for the TypeScript compiler to infer the structures in your code - so automatically generating a definition based on JavaScript is rarely an option.

There are instructions on how to write them from scratch here:

https://www.stevefenton.co.uk/2013/01/complex-typescript-definitions-made-easy/

But there is one trick that might work (it only works in a limited set of cases).

If you paste the JavaScript into a new TypeScript file, fix any trivial errors you may get and compile it using the definition flag, it may be able to get you a file that would at least be a starting point.

tsc --declaration js.ts

Upvotes: 81

tarling
tarling

Reputation: 1957

For my particular situation, where I was working with obfuscated code from a third party, I found it useful to load the script in a page, and then use the console to log an instance of the obfuscated class. The console gives you a neat summary of the class methods and properties which you can copy and use as the starting point of a definition file.

> o = new ObfuscatedClass()
> console.log(o)
ObfuscatedClass
- methodA(a,b){some implementation}
- methodB(a,b){other implementation} etc

which you can copy paste and edit to

declare class ObfuscatedClass {

    methodA(a,b);
    methodB(a,b);

}

Upvotes: 5

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