Generating typescript declaration files from javascript
TypescriptTypescript Problem Overview
Say for example, you have a npm library, in my case mongoose, how would you go about generating d.ts files?
Typescript Solutions
Solution 1 - Typescript
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
Solution 2 - Typescript
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:
-
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
-
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.
Solution 3 - Typescript
For other people who find this post through google: there's a generator now by Microsoft itself: dts-gen.
Solution 4 - Typescript
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;
}
Solution 5 - Typescript
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);
}
Solution 6 - Typescript
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.