GitHub - quansync-dev/quansync: "Superposition" between sync and async

Create sync/async APIs with usable logic.

Quantum + Sync - "Superposition" between sync and async.

Typesafe
ESM, modern JavaScript
Zero dependencies

Heavily inspired by genasync by @loganfsmyth.

Why & How

Please refer to Anthony's blog post: Async, Sync, in Between.

Usage

import fs from 'node:fs'
import { quansync } from 'quansync'

// Create a quansync function by providing `sync` and `async` implementations
const readFile = quansync({
  sync: (path: string) => fs.readFileSync(path),
  async: (path: string) => fs.promises.readFile(path),
})

// Create a quansync function by providing a generator function
const myFunction = quansync(function* (filename) {
  // Use `yield*` to call another quansync function
  const code = yield* readFile(filename, 'utf8')

  return `// some custom prefix\n${code}`
})

// Use it as a sync function
const result = myFunction.sync('./some-file.js')

// Use it as an async function
const asyncResult = await myFunction.async('./some-file.js')

`getIsAsync`

Returns a boolean indicating whether the current execution is in async mode.

import { getIsAsync, quansync } from 'quansync'

const fn = quansync(function* () {
  const isAsync: boolean = yield* getIsAsync()
  console.log(isAsync)
})

fn.sync() // false
await fn() // true
await fn.async() // true

`all`

import { all, quansync } from 'quansync'

const loadFiles = quansync(function* () {
  return yield* all([
    readFile('./one.js'),
    readFile('./two.js'),
    readFile('./three.js'),
  ])
})

const results = loadFiles.sync()
const asyncResults = await loadFiles.async()

Build-time Macro

If you don't like the function* and yield* syntax, we also provide a build-time macro via unplugin-quansync allowing you use quansync with async/await syntax, while still able to get the sync version out of that.

Here is an example:

import fs from 'node:fs'
import { quansync } from 'quansync/macro'

// Create a quansync function by providing `sync` and `async` implementations
const readFile = quansync({
  sync: (path: string) => fs.readFileSync(path),
  async: (path: string) => fs.promises.readFile(path),
})

// Create a quansync function by providing an **async** function
const myFunction = quansync(async (filename) => {
  // Use `await` to call another quansync function
  const code = await readFile(filename, 'utf8')

  return `// some custom prefix\n${code}`
})

// Use it as a sync function
const result = myFunction.sync('./some-file.js')

// Use it as an async function
const asyncResult = await myFunction.async('./some-file.js')

For more details on usage, refer to unplugin-quansync's docs.

Benchmark

Run the following command to benchmark the performance of quansync:

pnpm run build && pnpm run benchmark

Benchmark results indicate that each yield incurs an overhead of approximately 150 ns, comparable to that of await sync(). (On Apple M1 Max)