Importing untyped JS modules

[jonrimmer]

I have been trying out the 1.5 beta, but I am confused about importing modules from 3rd-party JS libraries. As I understand it, TS is intended as a superset of JS so if, for example, I have a CommonJS library called foo.js, then in my app.ts, I should be able to do:

import foo from 'foo';

And this should be compiled (depending on my compile options) into a CommonJS require statement, which can then be consumed by Node, Browserify, etc.

This works in regular JavaScript (as compiled by Babel), but it does not work in TypeScript. I get a compiler error saying "Cannot find external module 'foo'".

I understand that I can maybe write a .ts.d file that describes this library, but what if I don't want to do this? What if I just want to import a module and use it, as I would in regular JS?

[igl]

Just doing let foo = require('foo') worked for me.
Not perfect but at least i see which modules need definitions later on.

[tinganho]

You need to declare a d.ts file. I think let foo = require('foo')will break intellisense support.

[mhegazy]

The TypeScript compiler needs to know the shape of your import to ensure any uses of the import are correctly typed. consider this:

import foo from "module";
foo.a = 1;    // does foo has an export "a", and if so is it really a number

The compiler can not just look into the .js file, cause the .js file does not have any type annotations and thus most inferences will degenerate to any, which is not that helpful.

Instead, you need a different means to tell the compiler the shape of the module, its exports, and their types. that is the .d.ts as @tinganho mentioned earlier.

There is a community repository of definition files (.d.ts) for popular libraries on http://definitelytyped.org/; If your library is not there, you can hand edit a .d.ts file for it following this wiki page or use a tool like closure-ts that is d.ts generator from JSDoc typings.

[MicahZoltu]

I believe @jonrimmer and I both are wanting to know how to silence that error, perhaps with some kind of #prgama in the file? This is particularly meaningful for transitioning projects from ES6 to TypeScript.

Given the example import foo from "module";, I want a way to tell the TS compiler that I know there is no type definition for this and I accept that foo will be any. Maybe something like proposed here: #2709 (comment)

import foo: any from "module"; This would allow me to silence the warning while I work on migrating my project over to TypeScript. When I have an actual d.ts or ts file to work with, I can remove the : any. Even better would be if TypeScript gave me a warning if it was able to find module and it turns out that foo is not any. This way, while migrating I would have the safety of the static analyzer yelling at me if I forgot to remove the : any from any of my imports.

[mhegazy]

@Zoltu i believe this is fair. #2709 tracks this and should be simple to add.

[zakhenry]

FYI #2709 has been superseded by #6615

[alcfeoh]

This article brings great solutions to the problem: https://www.stevefenton.co.uk/2013/01/complex-typescript-definitions-made-easy/

[MicahZoltu]

I have been out of the TypeScript for a while, but at the time I participated in this discussion Definitely Typed didn't solve the problem primarily because it was unversioned. It was way too easy to pull in a definitely typed TSD only to find out (after 4 hours of debugging) that the definition it provided didn't match the definition of the version of the library you were using. Also, the tooling (again, at the time) wasn't very good in the browser world when it came to keeping TSDs and dependencies in sync.

[sjatkins]

In what sense is Typescript a mere superset if it forces me to create type files for all my pre-existing javascript modules? The easy interoperability is basically a lie. This is especially so for modules I have only minified versions of.

[mhegazy]

In what sense is Typescript a mere superset if it forces me to create type files for all my pre-existing javascript modules? The easy interoperability is basically a lie. This is especially so for modules I have only minified versions of.

Why does it "force" you?