76 lines
1.5 KiB
Markdown
76 lines
1.5 KiB
Markdown
---
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title: co
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category: JavaScript libraries
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updated: 2017-10-27
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weight: -1
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intro: |
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[co](https://github.com/tj/co) allows you to use generators to manage async flow.
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---
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[co]: https://github.com/tj/co
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[thunkify]: https://github.com/visionmedia/node-thunkify
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[unyield]: https://github.com/MatthewMueller/unyield
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[thenify]: https://www.npmjs.com/package/thenify
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[mz]: https://www.npmjs.com/package/mz
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### Running generators
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```js
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co(function * () {
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yield Promise.resolve(true)
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}).then(...)
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```
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A generator can `yield` a thunk or promise. Using `co()` will immediately invoke the block inside it.
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### Generator → Promise
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```js
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var fn = co.wrap(function * (val) {
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return yield Promise.resolve(val)
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})
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fn().then(...)
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```
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Use `co.wrap()`. Most of the time, you'll be using co.wrap.
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### Generator → Node callback
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```js
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var get = unyield(function * () {
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})
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get(function (err, res) { ... })
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```
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Use [unyield]. (You can [thunkify] this later)
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### Node callback → Thunk
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```js
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var readFile = thunkify(fs.readFile)
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co(function * () {
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var data = yield readFile('index.txt', 'utf-8')
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})
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```
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Use [thunkify]. You can yield this. You can also use [thenify] too.
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### Using Node.js API
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```js
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var readFile = require('mz/fs').readFile
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var getLines = co.wrap(function * (filename) {
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var data = yield readFile(filename, 'utf-8')
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return data.split('\n')
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})
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getLines('file.txt').then((lines) => { ... })
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```
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Use [mz] for async Node.js API. You can also either [thunkify] or [thenify] them instead.
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