How to use an node module without typings from Typescript

Question

I'm trying to import an external module from node_modules by just doing:

import { offline } from 'redux-offline';

From a file /src/store/store.ts. However, I get the following error:

Cannot find module redux-offline

I've read that we can declare a module, something like redux-offline.d.ts where we define sort of a dummy declaration that we can then use from our source code. Yet, I don't get it at all:

• In which folder should that file be defined?
• How does Typescript know that that module is declaring the interface of an external module?

I'd appreciate your help to understand how it works.

Answer 1

In which folder should that file be defined?

The files could really be declared in any folder however, it's good to put them together, in a directory that describes what they are. In our projects, we have a folder called "ambient-types" and within that we have an "external-modules" folder.

I've read that we can declare a module, something like redux-offline.d.ts

You're right, This would sit within the external-modules folder.

How does Typescript know that that module is declaring the interface of an external module?

In you're redux-offline.d.ts file we declare what's called an ambient declaration, it would look as follows:

declare module 'redux-offline';

redux-offline will now be available for import from your own files.

import { redux-offline } from 'redux-offline';

This basically tells Typescript that at runtime you expect that there will be a file/library called redux-offline available. Note that the import will have an "any" type.

Ambient declarations is a promise that you are making with the compiler. If these do not exist at runtime and you try to use them, things will break without warning.

For more reference see - https://basarat.gitbooks.io/typescript/docs/types/ambient/d.ts.html https://www.typescriptlang.org/docs/handbook/modules.html