2025-04-15 16:39:47 +02:00

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# quansync
[![npm version][npm-version-src]][npm-version-href]
[![npm downloads][npm-downloads-src]][npm-downloads-href]
[![bundle][bundle-src]][bundle-href]
[![JSDocs][jsdocs-src]][jsdocs-href]
[![License][license-src]][license-href]
Create sync/async APIs with usable logic.
**Quan**tum + **Sync** - "_Superposition_" between `sync` and `async`.
- Typesafe
- ESM, modern JavaScript
- Zero dependencies
Heavily inspired by [`genasync`](https://github.com/loganfsmyth/gensync) by [@loganfsmyth](https://github.com/loganfsmyth).
## Why & How
Please refer to Anthony's blog post: [**Async, Sync, in Between**](https://antfu.me/posts/async-sync-in-between).
## Usage
```bash
pnpm i quansync
```
```ts
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${code}`
})
// Use it as a sync function
const result = myFunction.sync('./some-file.js')
// Use it as an async function
const asyncResult = await myFunction.async('./some-file.js')
```
### `getIsAsync`
Returns a boolean indicating whether the current execution is in async mode.
```ts
import { getIsAsync, quansync } from 'quansync'
const fn = quansync(function* () {
const isAsync: boolean = yield* getIsAsync()
console.log(isAsync)
})
fn.sync() // false
await fn() // true
await fn.async() // true
```
## Build-time Macro
If you don't like the `function*` and `yield*` syntax, we also provide a build-time macro via [unplugin-quansync](https://github.com/unplugin/unplugin-quansync#usage) allowing you use quansync with async/await syntax, while still able to get the sync version out of that.
Here is an example:
```ts
import fs from 'node:fs'
import { quansync } from 'quansync/macro'
// Create a quansync function by providing `sync` and `async` implementations
const readFile = quansync({
sync: (path: string) => fs.readFileSync(path),
async: (path: string) => fs.promises.readFile(path),
})
// Create a quansync function by providing an **async** function
const myFunction = quansync(async (filename) => {
// Use `await` to call another quansync function
const code = await readFile(filename, 'utf8')
return `// some custom prefix\n${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](https://github.com/unplugin/unplugin-quansync#usage).
## Benchmark
Run the following command to benchmark the performance of `quansync`:
```bash
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)
## Sponsors
<p align="center">
<a href="https://cdn.jsdelivr.net/gh/antfu/static/sponsors.svg">
<img src='https://cdn.jsdelivr.net/gh/antfu/static/sponsors.svg'/>
</a>
</p>
<p align="center">
<a href="https://cdn.jsdelivr.net/gh/sxzz/sponsors/sponsors.svg">
<img src='https://cdn.jsdelivr.net/gh/sxzz/sponsors/sponsors.svg'/>
</a>
</p>
## License
[MIT](./LICENSE) License © [Anthony Fu](https://github.com/antfu) and [Kevin Deng](https://github.com/sxzz)
<!-- Badges -->
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[npm-downloads-src]: https://img.shields.io/npm/dm/quansync?style=flat&colorA=080f12&colorB=1fa669
[npm-downloads-href]: https://npmjs.com/package/quansync
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[license-href]: https://github.com/antfu/quansync/blob/main/LICENSE
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[jsdocs-href]: https://www.jsdocs.io/package/quansync