pending-queue

library1.2.1jsnpmunverified

A lightweight queue that ensures a given asynchronous function (load) is executed only once for a given set of parameters, while multiple callers can await the result. Version 1.2.1 is the latest stable release. The package is minimal (zero dependencies) and designed for Node.js 4+. It provides an EventEmitter-based API and custom key serialization via stringify. Use cases include deduplicating API calls, database queries, or any expensive async operation. Unlike similar deduplication utilities, pending-queue queues listeners rather than memoizing results, making it suitable for one-shot or short-lived caching.

devops

npm install pending-queue

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INSTALL

IMPORT

SIG · PENDING-QUEUE

pending-queue

devopsjavascriptv1.2.1

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

Queue

✓ const Queue = require('pending-queue')

✗ import Queue from 'pending-queue'

This package does not provide ESM exports; use require() in Node.js.

Queue (with options)

✓ const queue = new (require('pending-queue'))({ load: fn })

✗ const queue = require('pending-queue').default({ load: fn })

The module exports a constructor directly; no default or named exports.

Queue add method

✓ queue.add(1, 2).then(console.log)

✗ queue.add([1, 2]).then(console.log)

add() takes spread arguments, not an array; it will pass them to the load function.

Demonstrates deduplication: three calls to .add(1,2) share a single execution of the load function.

const Queue = require('pending-queue'); const queue = new Queue({ load: (a, b) => new Promise(resolve => setTimeout(() => resolve(a + b), 100)) }); queue.add(1, 2).then(value => console.log('First:', value)); queue.add(1, 2).then(value => console.log('Second:', value)); queue.add(1, 2).then(value => console.log('Third:', value)); // All three resolve with 3, but load runs only once.

Debug

Known issues

gotchaParameters must be serializable deterministically (default uses JSON.stringify). Non-JSON-safe objects (dates, regex, etc.) may cause mismatched keys.

fix

Provide a custom stringify function or use addWithKey with an explicit key.

affects: >=1.0.0

gotchaThe queue does not expire; if load never resolves or rejects, .add() promises will hang forever.

fix

Ensure load always settles or implement a timeout externally.

affects: >=1.0.0

gotchaEvent names are derived from serialized keys (default JSON string). If keys are long or contain special characters, they may interfere with EventEmitter behavior.

fix

Use addWithKey with a safe key string.

affects: >=1.0.0

Errors

Common errors & fixes

TypeError: pending_queue is not a constructor

Using ESM import syntax with this CommonJS-only module.

fix

Replace `import Queue from 'pending-queue'` with `const Queue = require('pending-queue')`.

TypeError: queue.add is not a function

Calling `add()` before instantiating the Queue (e.g., `const queue = require('pending-queue').add(...)`).

fix

Instantiate with `new Queue({ load: ... })` then call `.add()`.

UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: x): Error

The load function threw an error or returned a rejected promise, and no .catch() is attached to the add() promise.

fix

Attach a .catch() to each .add() call or use the 'error' event on the queue.

Upgrade

Version history

1.2.1latest on npm

Audit

Dependencies

No dependency data recorded yet.

Agent activity

2 hits · last 30 days

node

Resources

githubgit://github.com/kaelzhang/node-pending-queue ↗

packagepending-queue ↗

homepagehttps://github.com/kaelzhang/node-pending-queue#readme ↗