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https://github.com/tj/co

The ultimate generator based flow-control goodness for nodejs (supports thunks, promises, etc)
https://github.com/tj/co

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The ultimate generator based flow-control goodness for nodejs (supports thunks, promises, etc)

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# co



[![Gitter][gitter-image]][gitter-url]

[![NPM version][npm-image]][npm-url]

[![Build status][travis-image]][travis-url]

[![Test coverage][coveralls-image]][coveralls-url]

[![Downloads][downloads-image]][downloads-url]



  Generator based control flow goodness for nodejs and the browser,

  using promises, letting you write non-blocking code in a nice-ish way.



## Co v4



  `[email protected]` has been released, which now relies on promises.

  It is a stepping stone towards the [async/await proposal](https://github.com/lukehoban/ecmascript-asyncawait).

  The primary API change is how `co()` is invoked.

  Before, `co` returned a "thunk", which you then called with a callback and optional arguments.

  Now, `co()` returns a promise.



```js

co(function* () {

  var result = yield Promise.resolve(true);

  return result;

}).then(function (value) {

  console.log(value);

}, function (err) {

  console.error(err.stack);

});

```



  If you want to convert a `co`-generator-function into a regular function that returns a promise,

  you now use `co.wrap(fn*)`.



```js

var fn = co.wrap(function* (val) {

  return yield Promise.resolve(val);

});



fn(true).then(function (val) {



});

```



## Platform Compatibility



  `co@4+` requires a `Promise` implementation.

  For versions of node `< 0.11` and for many older browsers,

  you should/must include your own `Promise` polyfill.



  When using node 0.10.x and lower or browsers without generator support,

  you must use [gnode](https://github.com/TooTallNate/gnode) and/or [regenerator](http://facebook.github.io/regenerator/).



  When using node 0.11.x, you must use the `--harmony-generators`

  flag or just `--harmony` to get access to generators.



  Node v4+ is supported out of the box, you can use `co` without flags or polyfills.



## Installation



```

$ npm install co

```



## Associated libraries



Any library that returns promises work well with `co`.



- [mz](https://github.com/normalize/mz) - wrap all of node's code libraries as promises.



View the [wiki](https://github.com/visionmedia/co/wiki) for more libraries.



## Examples



```js

var co = require('co');



co(function *(){

  // yield any promise

  var result = yield Promise.resolve(true);

}).catch(onerror);



co(function *(){

  // resolve multiple promises in parallel

  var a = Promise.resolve(1);

  var b = Promise.resolve(2);

  var c = Promise.resolve(3);

  var res = yield [a, b, c];

  console.log(res);

  // => [1, 2, 3]

}).catch(onerror);



// errors can be try/catched

co(function *(){

  try {

    yield Promise.reject(new Error('boom'));

  } catch (err) {

    console.error(err.message); // "boom"

 }

}).catch(onerror);



function onerror(err) {

  // log any uncaught errors

  // co will not throw any errors you do not handle!!!

  // HANDLE ALL YOUR ERRORS!!!

  console.error(err.stack);

}

```



## Yieldables



  The `yieldable` objects currently supported are:



  - promises

  - thunks (functions)

  - array (parallel execution)

  - objects (parallel execution)

  - generators (delegation)

  - generator functions (delegation)



Nested `yieldable` objects are supported, meaning you can nest

promises within objects within arrays, and so on!



### Promises



[Read more on promises!](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)



### Thunks



Thunks are functions that only have a single argument, a callback.

Thunk support only remains for backwards compatibility and may

be removed in future versions of `co`.



### Arrays



`yield`ing an array will resolve all the `yieldables` in parallel.



```js

co(function* () {

  var res = yield [

    Promise.resolve(1),

    Promise.resolve(2),

    Promise.resolve(3),

  ];

  console.log(res); // => [1, 2, 3]

}).catch(onerror);

```



### Objects



Just like arrays, objects resolve all `yieldable`s in parallel.



```js

co(function* () {

  var res = yield {

    1: Promise.resolve(1),

    2: Promise.resolve(2),

  };

  console.log(res); // => { 1: 1, 2: 2 }

}).catch(onerror);

```



### Generators and Generator Functions



Any generator or generator function you can pass into `co`

can be yielded as well. This should generally be avoided

as we should be moving towards spec-compliant `Promise`s instead.



## API



### co(fn*).then( val => )



Returns a promise that resolves a generator, generator function,

or any function that returns a generator.



```js

co(function* () {

  return yield Promise.resolve(true);

}).then(function (val) {

  console.log(val);

}, function (err) {

  console.error(err.stack);

});

```



### var fn = co.wrap(fn*)



Convert a generator into a regular function that returns a `Promise`.



```js

var fn = co.wrap(function* (val) {

  return yield Promise.resolve(val);

});



fn(true).then(function (val) {



});

```



## License



  MIT



[npm-image]: https://img.shields.io/npm/v/co.svg?style=flat-square

[npm-url]: https://npmjs.org/package/co

[travis-image]: https://img.shields.io/travis/tj/co.svg?style=flat-square

[travis-url]: https://travis-ci.org/tj/co

[coveralls-image]: https://img.shields.io/coveralls/tj/co.svg?style=flat-square

[coveralls-url]: https://coveralls.io/r/tj/co

[downloads-image]: http://img.shields.io/npm/dm/co.svg?style=flat-square

[downloads-url]: https://npmjs.org/package/co

[gitter-image]: https://badges.gitter.im/Join%20Chat.svg

[gitter-url]: https://gitter.im/tj/co?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge