# thunky

> delay the evaluation of a paramless async function and cache the result

Latest version **1.1.0** (published 2019-10-14) · MIT license · 0 weekly downloads

## Install

```sh
npm install thunky
pnpm add thunky
yarn add thunky
bun add thunky
```

## Health

**Score 23/100 (F)** — status: abandoned.

Positive: has types package; no vulnerabilities; high quality score.

Warnings: low downloads; no esm support.

Negative: abandoned; low maintenance score.

## Facts

| | |
|---|---|
| Version | 1.1.0 |
| Published | 2019-10-14 |
| First published | 2013-03-06 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | separate (@types/thunky) |
| Module format | CommonJS |
| Dependencies | 0 |
| Unpacked size | 7.6 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| GitHub stars | 94 |
| Author | Mathias Buus Madsen |
| Maintainers | feross, mafintosh |
| Keywords | memo, thunk, async, lazy, control, flow, cache |

## Links

- npm: https://www.npmjs.com/package/thunky
- Repository: https://github.com/mafintosh/thunky
- Homepage: https://github.com/mafintosh/thunky#readme
- Issues: https://github.com/mafintosh/thunky/issues
- npm.io page: https://npm.io/package/thunky

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## Recent versions

- 1.1.0 (latest) — 2019-10-14
- 1.0.3 — 2018-10-16
- 1.0.2 — 2017-02-12
- 1.0.1 — 2016-07-15
- 1.0.0 — 2016-07-15
- 0.1.0 — 2013-03-06

## README

# thunky

Delay the evaluation of a paramless async function and cache the result (see [thunk](http://en.wikipedia.org/wiki/Thunk_%28functional_programming%29)).

```
npm install thunky
```

[![build status](http://img.shields.io/travis/mafintosh/thunky.svg?style=flat)](http://travis-ci.org/mafintosh/thunky)

## Example

Let's make a simple function that returns a random number 1 second after it is called for the first time

``` js
var thunky = require('thunky')

var test = thunky(function (callback) { // the inner function should only accept a callback
  console.log('waiting 1s and returning random number')
  setTimeout(function () {
    callback(Math.random())
  }, 1000)
})

test(function (num) {  // inner function is called the first time we call test
  console.log(num) // prints random number
})

test(function (num) {  // subsequent calls waits for the first call to finish and return the same value
  console.log(num) // prints the same random number as above
})
```

## Lazy evaluation

Thunky makes it easy to implement a lazy evaluation pattern.

``` js
var getDb = thunky(function (callback) {
  db.open(myConnectionString, callback)
})

var queryDb = function (query, callback) {
  getDb(function (err, db) {
    if (err) return callback(err)
    db.query(query, callback)
  })
}

queryDb('some query', function (err, result) { ... } )

queryDb('some other query', function (err, result) { ... } )
```

The first time `getDb` is called it will try do open a connection to the database.
Any subsequent calls will just wait for the first call to complete and then call your callback.

A nice property of this pattern is that it *easily* allows us to pass any error caused by `getDb` to the `queryDb` callback.

## Error → No caching

If the thunk callback is called with an `Error` object as the first argument it will not cache the result

``` js
var fails = thunky(function (callback) {
  console.log('returning an error')
  callback(new Error('bad stuff'))
})

fails(function (err) { // inner function is called
  console.log(err)
});

fails(function (err) { // inner function is called again as it returned an error before
  console.log(err)
})
```

## Promise version

A promise version is available as well

``` js
var thunkyp = require('thunky/promise')

var ready = thunkyp(async function () {
  // ... do async stuff
  return 42
})

// same semantics as the callback version
await ready()
```

## License

MIT

---
_Source: https://npm.io/package/thunky · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._