Cannot import module

Question

I have the following code:

import {AsyncLock} from 'async-lock';

but tsc is complaining:

[ts] Module '"my_app/node_modules/@types/async-lock/index"' has no exported member 'AsyncLock'.

but if I look at my_app/node_modules/@types/async-lock/index.d.ts I see the following:

interface AsyncLockDoneCallback {
    (err?: Error, ret?: any): void;
}

interface AsyncLockOptions {
    timeout?: number;
    maxPending?: number;
    domainReentrant?: boolean;
    Promise?: any;
}

declare class AsyncLock {
    constructor(options?: AsyncLockOptions);

    acquire(key: string | string[], fn: (done: AsyncLockDoneCallback) 
=> any, cb: AsyncLockDoneCallback, opts?: AsyncLockOptions): void;
    acquire(key: string | string[], fn: (done: AsyncLockDoneCallback) 
=> any, opts?: AsyncLockOptions): PromiseLike<any>;

    isBusy(): boolean;
}

declare namespace AsyncLock { }

export = AsyncLock;

It very much looks to me as if AsyncLock is being exported here. Where am I going wrong with my import definition?

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

Short Answer

When a declaration file exports like this:

export = AsyncLock;

Then we import it in one of these two ways:

import AsyncLock = require("async-lock"); // thank you unional
import * as AsyncLock from "async-lock";

Both support static analysis. (See unional's corrections below in the comments.)

Further Details

From the TypeScript modules documentation:

Both CommonJS and AMD generally have the concept of an exports object which contains all exports from a module.

They also support replacing the exports object with a custom single object. Default exports are meant to act as a replacement for this behavior; however, the two are incompatible. TypeScript supports export = to model the traditional CommonJS and AMD workflow.

What you were trying to use is the more modern style, when a declaration file exports like this:

export { AsyncLock }

In that case, we do import it like this:

import { AsyncLock } from "async-lock";

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Aug 5, 2017 at 23:14

Shaun Luttin

143k93 gold badges443 silver badges495 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

unional Over a year ago

Note that NodeJS is going against this, and prefer import x = require('async-lock')

Shaun Luttin Over a year ago

@unional My sense is that using require(...) is deprecated in favor of the new ECMA module system. For instance MDN developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… does not mention require(...), nor does the ECMAScript living standard tc39.github.io/ecma262 Also, the NodeJS docs mark require(...) as deprecated nodejs.org/api/modules.html#modules_require

unional Over a year ago

It is mentioned in github.com/nodejs/node-eps/issues. It's a topic span across multiple issues and you can start from here github.com/Microsoft/TypeScript/issues/16093 and follow the links. The bottom line here is the interop syntax was not defined by tc39 and TS and NodeJS/Babel/SystemJS goes in different ways. We now need to find a way to fix this issue.

unional Over a year ago

Also, the "deprecated" part in nodejs.org is the require.extensions, not require() itself.

unional Over a year ago

Another note that require() will never be on MDN nor ECMAScript living standard because it is part of module loader, not part of the language. We would like to migrate to ESM, but we first need to solve the migration issue from CJS to ESM.

|

Collectives™ on Stack Overflow

Cannot import module

1 Answer 1

Short Answer

Further Details

7 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Short Answer

Further Details

7 Comments

Your Answer

Sign up or log in

Post as a guest

Related