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,
you now use co.wrap(fn*).
```js var fn = co.wrap(function* (val) { return yield Promise.resolve(val); });
fn(true).then(function (val) {
}); ```
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 0.11.x or greater, you must use the --harmony-generators
flag or just --harmony 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.
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:
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 Promises 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