node-singleflight

Suppress duplicate function calls with the same key while one call is still in flight. Duplicate callers share the same result or rejection.

Install

npm install node-singleflight

yarn add node-singleflight

Usage

JavaScript using the existing CommonJS API:

const singleflight = require('node-singleflight')

async function example() {
  return singleflight.Do('SomeKey', async () => {
    const data = await doSomething()
    return processData(data)
  })
}

The equivalent TypeScript version uses the declarations included with the package:

import { Do } from 'node-singleflight'

async function example(): Promise<ProcessedData> {
  return Do('SomeKey', async () => {
    const data = await doSomething()
    return processData(data)
  })
}

API

Do(key, func)

Runs func once while the given key is in flight and returns a Promise for its result.

• Calls with the same key share the same result or rejection.
• Calls with different keys run independently.
• Keys use JavaScript Map identity semantics; object keys match by reference.
• The key is removed after fulfillment or rejection, so a later call can retry.
• func may return a value, a Promise, or any Promise-like value.

func must eventually settle. If it never fulfills or rejects, calls using the same key will continue waiting. Apply a timeout or cancellation inside func when the underlying operation can hang.