generator async control flow goodness
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Generator based control flow goodness for nodejs and the browser,
using promises, letting you write non-blocking code in a nice-ish way.
co@4.0.0 has been released, which now relies on promises.
It is a stepping stone towards ES7 async/await.
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,co.wrap(fn*)
you now use .
`js
var fn = co.wrap(function* (val) {
return yield Promise.resolve(val);
});
fn(true).then(function (val) {
});
`
co@4+ requires a Promise implementation.< 0.11
For versions of node and for many older browsers,Promise
you should/must include your own polyfill.
When using node 0.11.x or greater, you must use the --harmony-generators
flag or just to get access to generators.
When using node 0.10.x and lower or browsers without generator support,
you must use gnode and/or regenerator.
io.js is supported out of the box, you can use co without flags or polyfills.
`
$ npm install co
Any library that returns promises work well with co.
- mz - wrap all of node's code libraries as promises.
View the wiki for more libraries.
`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);
}
`
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!
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.
yielding 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);
Just like arrays, objects resolve all yieldables 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);
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 s instead.
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);
});
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) {
});
``
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
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[coveralls-url]: https://coveralls.io/r/tj/co
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[downloads-url]: https://npmjs.org/package/co
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