Overview

Yaku is full compatible with ES6's native Promise, but much faster, and more error friendly. If you want to learn how Promise works, read the minimum implementation docs/minPromiseA+.coffee. Without comments, it is only 80 lines of code (gzipped size is 0.5KB). It only implements the constructor and then. It passed all the tests of promises-aplus-tests.

I am not an optimization freak, I try to keep the source code readable and maintainable. Premature optimization is the root of all evil. I write this lib to research one of my data structure ideas: docs/lazyTree.md.

Features

The minified file is only 3.5KB (1.5KB gzipped) (Bluebird / 73KB, ES6-promise / 18KB)
Better "possibly unhandled rejection" and "long stack trace" than Bluebird
Much better performance than the native Promise
100% compliant with Promises/A+ specs and ES6
Designed to work on IE5+ and other major browsers
Well commented source code with every Promises/A+ spec

Quick Start

Node.js

npm install yaku

Then:

var Promise = require('yaku');

Browser

Use something like Browserify or Webpack, or download the yaku.js file from release page. Raw usage without:

<script type="text/javascript" src ="yaku.js"></script>
<script>
    // Yaku will be assigned to `window.Yaku`.
    var Promise = Yaku;
</script>

Change Log

docs/changelog.md

Compare to Other Promise Libs

These comparisons only reflect some limited truth, no one is better than all others on all aspects. For more details see the benchmark/readme.md. There are tons of Promises/A+ implementations, you can see them here. Only some of the famous ones were tested.

Name	1ms async task / mem	sync task / mem	Helpers	file size
Yaku	257ms / 110MB	126ms / 80MB	+++	3.5KB
Bluebird v2.9	249ms / 102MB	155ms / 80MB	+++++++	73KB
ES6-promise v2.3	427ms / 120MB	92ms / 78MB	+	18KB
native iojs v1.8	789ms / 189MB	605ms / 147MB	+	0KB
q v1.3	2648ms / 646MB	2373ms / 580MB	+++	24K

Helpers: extra methods that help with your promise programming, such as async flow control helpers, debug helpers. For more details: docs/debugHelperComparison.md.
1ms async task: npm run no -- benchmark, the smaller the better.
sync task: npm run no -- benchmark --sync, the smaller the better.

FAQ

catch on old brwoser (IE7, IE8 etc)?

In ECMA-262 spec, catch cannot be used as method name. You have to alias the method name or use something like Promise.resolve()['catch'](function() {}) or Promise.resolve().then(null, function() {}).
Will Yaku implement done, finally, promisify, etc?

No. All non-ES6 APIs are only implemented for debugging and testing, which means when you remove Yaku, everything should work well with ES6 native promise. If you need fancy and magic, go for Bluebird.
When using with Babel and Regenerator, the unhandled rejection doesn't work.

Because Regenerator use global Promise directly and don't have an api to set the Promise lib. You have to import Yaku globally to make it use Yaku: require("yaku/lib/global");.
Better long stack trace support?

Latest Node.js and browsers are already support it. If you enabled it, Yaku will take advantage of it without much overhead. Such as this library longjohn for Node.js, or this article for Chrome.
The name Yaku is weird?

The name yaku comes from the word 約束(yakusoku) which means promise.

Unhandled Rejection

Yaku will report any unhandled rejection via console.error by default, in case you forget to write catch. You can catch with them manually:

Browser: window.onunhandledrejection = ({ promise, reason }) => { /* Your Code */ };
Node: process.on("unhandledRejection", (reason, promise) => { /* Your Code */ });

For more spec read Unhandled Rejection Tracking Browser Events.

API

Yaku(executor)

This class follows the Promises/A+ and ES6 spec with some extra helpers.

param: executor { Function }

Function object with three arguments resolve, reject and the promise itself. The first argument fulfills the promise, the second argument rejects it. We can call these functions, once our operation is completed. The this context of the executor is the promise itself, it can be used to add custom handlers, such as abort or progress helpers.

example:

Here's an abort example.

var Promise = require('yaku');
var p = new Promise((resolve, reject) => {
    var tmr = setTimeout(resolve, 3000);
    this.abort = (reason) => {
        clearTimeout(tmr);
        reject(reason);
    };
});

p.abort(new Error('abort'));

example:

Here's a progress example.

var Promise = require('yaku');
var p = new Promise((resolve, reject) => {
    var self = this;
    var count = 0;
    var all = 100;
    var tmr = setInterval(() => {
        try {
            self.progress && self.progress(count, all);
        } catch (err) {
            reject(err);
        }

        if (count < all)
            count++;
        else {
            resolve();
            clearInterval(tmr);
        }
    }, 1000);
});

p.progress = (curr, all) => {
    console.log(curr, '/', all);
};

then(onFulfilled, onRejected)

Appends fulfillment and rejection handlers to the promise, and returns a new promise resolving to the return value of the called handler.
- param: onFulfilled { Function }
  
  Optional. Called when the Promise is resolved.
- param: onRejected { Function }
  
  Optional. Called when the Promise is rejected.
- return: { Yaku }
  
  It will return a new Yaku which will resolve or reject after
- example:
  
  the current Promise.
```
var Promise = require('yaku');
var p = Promise.resolve(10);

p.then((v) => {
    console.log(v);
});
```
catch(onRejected)

The catch() method returns a Promise and deals with rejected cases only. It behaves the same as calling Promise.prototype.then(undefined, onRejected).
- param: onRejected { Function }
  
  A Function called when the Promise is rejected. This function has one argument, the rejection reason.
- return: { Yaku }
  
  A Promise that deals with rejected cases only.
- example:
```
var Promise = require('yaku');
var p = Promise.reject(new Error("ERR"));

p['catch']((v) => {
    console.log(v);
});
```
Yaku.resolve(value)

The Promise.resolve(value) method returns a Promise object that is resolved with the given value. If the value is a thenable (i.e. has a then method), the returned promise will "follow" that thenable, adopting its eventual state; otherwise the returned promise will be fulfilled with the value.
- param: value { Any }
  
  Argument to be resolved by this Promise. Can also be a Promise or a thenable to resolve.
- return: { Yaku }
- example:
```
var Promise = require('yaku');
var p = Promise.resolve(10);
```
Yaku.reject(reason)

The Promise.reject(reason) method returns a Promise object that is rejected with the given reason.
- param: reason { Any }
  
  Reason why this Promise rejected.
- return: { Yaku }
- example:
```
var Promise = require('yaku');
var p = Promise.reject(new Error("ERR"));
```
Yaku.race(iterable)

The Promise.race(iterable) method returns a promise that resolves or rejects as soon as one of the promises in the iterable resolves or rejects, with the value or reason from that promise.
- param: iterable { iterable }
  
  An iterable object, such as an Array.
- return: { Yaku }
  
  The race function returns a Promise that is settled the same way as the first passed promise to settle. It resolves or rejects, whichever happens first.
- example:
```
var Promise = require('yaku');
Promise.race([
    123,
    Promise.resolve(0)
])
.then((value) => {
    console.log(value); // => 123
});
```
Yaku.all(iterable)

The Promise.all(iterable) method returns a promise that resolves when all of the promises in the iterable argument have resolved.

The result is passed as an array of values from all the promises. If something passed in the iterable array is not a promise, it's converted to one by Promise.resolve. If any of the passed in promises rejects, the all Promise immediately rejects with the value of the promise that rejected, discarding all the other promises whether or not they have resolved.
- param: iterable { iterable }
  
  An iterable object, such as an Array.
- return: { Yaku }
- example:
```
var Promise = require('yaku');
Promise.all([
    123,
    Promise.resolve(0)
])
.then((values) => {
    console.log(values); // => [123, 0]
});
```
- example:
  
  Use with iterable.
```
var Promise = require('yaku');
Promise.all((function * () {
    yield 10;
    yield new Promise(function (r) { setTimeout(r, 1000, "OK") });
})())
.then((values) => {
    console.log(values); // => [123, 0]
});
```
Yaku.Symbol

The ES6 Symbol object that Yaku should use, by default it will use the global one.
- type: { Object }
- example:
```
var core = require("core-js/library");
var Promise = require("yaku");
Promise.Symbol = core.Symbol;
```

Yaku.onUnhandledRejection(reason, p)

Catch all possibly unhandled rejections. If you want to use specific format to display the error stack, overwrite it. If it is set, auto console.error unhandled rejection will be disabled.

param: reason { Any }

The rejection reason.
param: p { Yaku }

The promise that was rejected.

example:

var Promise = require('yaku');
Promise.onUnhandledRejection = (reason) => {
    console.error(reason);
};

// The console will log an unhandled rejection error message.
Promise.reject('my reason');

// The below won't log the unhandled rejection error message.
Promise.reject('v').catch(() => {});

Yaku.enableLongStackTrace

It is used to enable the long stack trace. Once it is enabled, it can't be reverted. While it is very helpful in development and testing environments, it is not recommended to use it in production. It will slow down your application and waste your memory.
- example:
```
var Promise = require('yaku');
Promise.enableLongStackTrace();
```
Yaku.nextTick

Only Node has process.nextTick function. For browser there are so many ways to polyfill it. Yaku won't do it for you, instead you can choose what you prefer. For example, this project setImmediate. By default, Yaku will use process.nextTick on Node, setTimeout on browser.
- type: { Function }
- example:
```
var Promise = require('yaku');
Promise.nextTick = fn => window.setImmediate(fn);
```
- example:
  
  You can even use sync resolution if you really know what you are doing.
```
var Promise = require('yaku');
Promise.nextTick = fn => fn();
```
genIterator(obj)

Generate a iterator
- param: obj { Any }
- return: { Function }

Utils

It's a bundle of all the following functions. You can require them all with var yutils = require("yaku/lib/utils"), or require them separately like require("yaku/lib/flow"). If you want to use it in the browser, you have to use browserify or webpack. You can even use another Promise lib, such as:

require("yaku/lib/_").Promise = require("bluebird");
var source = require("yaku/lib/source");

// now "source" use bluebird instead of yaku.

any(iterable)

Similar with the Promise.race, but only rejects when every entry rejects.

param: iterable { iterable }

An iterable object, such as an Array.
return: { Yaku }

example:

var any = require('yaku/lib/any');
any([
    123,
    Promise.resolve(0),
    Promise.reject(new Error("ERR"))
])
.then((value) => {
    console.log(value); // => 123
});

async(limit, list, saveResults, progress)

A function that helps run functions under a concurrent limitation. To run functions sequentially, use yaku/lib/flow.

param: limit { Int }

The max task to run at a time. It's optional. Default is Infinity.
param: list { Iterable }

Any iterable object. It should be a lazy iteralbe object, don't pass in a normal Array with promises.
param: saveResults { Boolean }

Whether to save each promise's result or not. Default is true.
param: progress { Function }

If a task ends, the resolved value will be passed to this function.
return: { Promise }

example:

var kit = require('nokit');
var async = require('yaku/lib/async');

var urls = [
    'http://a.com',
    'http://b.com',
    'http://c.com',
    'http://d.com'
];
var tasks = function * () {
    var i = 0;
    yield kit.request(url[i++]);
    yield kit.request(url[i++]);
    yield kit.request(url[i++]);
    yield kit.request(url[i++]);
}();

async(tasks).then(() => kit.log('all done!'));

async(2, tasks).then(() => kit.log('max concurrent limit is 2'));

async(3, { next: () => {
    var url = urls.pop();
    return {
         done: !url,
         value: url && kit.request(url)
    };
} })
.then(() => kit.log('all done!'));

callbackify(fn, self)

If a function returns promise, convert it to node callback style function.
- param: fn { Function }
- param: self { Any }
  
  The this to bind to the fn.
- return: { Function }
Deferred

deprecate Create a jQuery.Deferred like object. It will cause some buggy problems, please don't use it.

flow(list)

Creates a function that is the composition of the provided functions. See yaku/lib/async, if you need concurrent support.

param: list { Iterable }

Any iterable object. It should be a lazy iteralbe object, don't pass in a normal Array with promises.
return: { Function }

(val) -> Promise A function that will return a promise.

example:

It helps to decouple sequential pipeline code logic.

var kit = require('nokit');
var flow = require('yaku/lib/flow');

function createUrl (name) {
    return "http://test.com/" + name;
}

function curl (url) {
    return kit.request(url).then((body) => {
        kit.log('get');
        return body;
    });
}

function save (str) {
    kit.outputFile('a.txt', str).then(() => {
        kit.log('saved');
    });
}

var download = flow(createUrl, curl, save);
// same as "download = flow([createUrl, curl, save])"

download('home');

example:

Walk through first link of each page.

var kit = require('nokit');
var flow = require('yaku/lib/flow');

var list = [];
function iter (url) {
    return {
        done: !url,
        value: url && kit.request(url).then((body) => {
            list.push(body);
            var m = body.match(/href="(.+?)"/);
            if (m) return m[0];
        });
    };
}

var walker = flow(iter);
walker('test.com');

isPromise(obj)

deprecate Check if an object is a promise-like object. Don't use it to coercive a value to Promise, instead use Promise.resolve.
- param: obj { Any }
- return: { Boolean }
never()

Create a promise that never ends.
- return: { Promise }
  
  A promise that will end the current pipeline.

promisify(fn, self)

Convert a node callback style function to a function that returns promise when the last callback is not supplied.

param: fn { Function }
param: self { Any }

The this to bind to the fn.
return: { Function }

example:

var promisify = require('yaku/lib/promisify');
function foo (val, cb) {
    setTimeout(() => {
        cb(null, val + 1);
    });
}

var bar = promisify(foo);

bar(0).then((val) => {
    console.log val // output => 1
});

// It also supports the callback style.
bar(0, (err, val) => {
    console.log(val); // output => 1
});

sleep(time, val)

Create a promise that will wait for a while before resolution.
- param: time { Integer }
  
  The unit is millisecond.
- param: val { Any }
  
  What the value this promise will resolve.
- return: { Promise }
- example:
```
var sleep = require('yaku/lib/sleep');
sleep(1000).then(() => console.log('after one second'));
```
Observable

Read the Observable section.
- type: { Function }
retry(countdown, fn, this)

Retry a function until it resolves before a mount of times, or reject with all the error states.
- version_added:
  
  v0.7.10
- param: countdown { Number | Function }
  
  How many times to retry before rejection. When it's a function (errs) => Boolean | Promise.resolve(Boolean), you can use it to create complex countdown logic, it can even return a promise to create async countdown logic.
- param: fn { Function }
  
  The function can return a promise or not.
- param: this { Any }
  
  Optional. The context to call the function.
- return: { Function }
  
  The wrapped function. The function will reject an array of reasons that throwed by each try.
- example:
  
  Retry 3 times before rejection.
```
var retry = require('yaku/lib/retry');
var { request } = require('nokit');

retry(3, request)('http://test.com').then(
   (body) => console.log(body),
   (errs) => console.error(errs)
);
```
- example:
  
  Here a more complex retry usage, it shows an random exponential backoff algorithm to wait and retry again, which means the 10th attempt may take 10 minutes to happen.
```
var retry = require('yaku/lib/retry');
var sleep = require('yaku/lib/sleep');
var { request } = require('nokit');

function countdown (retries) {
   var attempt = 0;
   return async () => {
        var r = Math.random() * Math.pow(2, attempt) * 1000;
        var t = Math.min(r, 1000 * 60 * 10);
        await sleep(t);
        return attempt++ < retries;
   };
}

retry(countdown(10), request)('http://test.com').then(
   (body) => console.log(body),
   (errs) => console.error(errs)
);
```

throw(err)

Throw an error to break the program.

param: err { Any }

example:

var ythrow = require('yaku/lib/throw');
Promise.resolve().then(() => {
    // This error won't be caught by promise.
    ythrow('break the program!');
});

Observable

Observable(executor)

Create a composable observable object. Promise can't resolve multiple times, this function makes it possible, so that you can easily map, filter and even back pressure events in a promise way. For real world example: Double Click Demo.

version_added:

v0.7.2
param: executor { Function }

(emit) -> It's optional.
return: { Observable }

example:

var Observable = require("yaku/lib/Observable");
var linear = new Observable();

var x = 0;
setInterval(linear.emit, 1000, x++);

// Wait for a moment then emit the value.
var quad = linear.subscribe(async x => {
    await sleep(2000);
    return x * x;
});

var another = linear.subscribe(x => -x);

quad.subscribe(
    value => { console.log(value); },
    reason => { console.error(reason); }
);

// Emit error
linear.emit(Promise.reject(new Error("reason")));

// Unsubscribe a observable.
quad.unsubscribe();

// Unsubscribe all subscribers.
linear.subscribers = [];

example:

Use it with DOM.

var filter = fn => v => fn(v) ? v : new Promise(() => {});

var keyup = new Observable((emit) => {
    document.querySelector('input').onkeyup = emit;
});

var keyupText = keyup.subscribe(e => e.target.value);

// Now we only get the input when the text length is greater than 3.
var keyupTextGT3 = keyupText.subscribe(filter(text => text.length > 3));

keyupTextGT3.subscribe(v => console.log(v));

emit(value)

Emit a value.
- param: value { Any }
value

The promise that will resolve current value.
- type: { Promise }
publisher

The publisher observable of this.
- type: { Observable }
subscribers

All the subscribers subscribed this observable.
- type: { Array }
subscribe(onEmit, onError)

It will create a new Observable, like promise.
- param: onEmit { Function }
- param: onError { Function }
- return: { Observable }
unsubscribe

Unsubscribe this.

Observable.merge(iterable)

Merge multiple observables into one.

version_added:

0.9.6
param: iterable { Iterable }
return: { Observable }

example:

var Observable = require("yaku/lib/Observable");
var sleep = require("yaku/lib/sleep");

var src = new Observable(emit => setInterval(emit, 1000, 0));

var a = src.subscribe(v => v + 1; });
var b = src.subscribe((v) => sleep(10, v + 2));

var out = Observable.merge([a, b]);

out.subscribe((v) => {
    console.log(v);
})

Unit Test

This project use promises-aplus-tests to test the compliance of Promises/A+ specification. There are about 900 test cases.

Use npm run no -- test to run the unit test.

Benchmark

Use npm run no -- benchmark to run the benchmark.

Contribute

Other than use gulp, all my projects use nokit to deal with automation. Run npm run no -- -h to print all the tasks that defined in the nofile.js. If you installed nokit globally, you can just run no -h without npm run and --.

jackiealex/yaku

Overview

Features

Quick Start

Node.js

Browser

Change Log

Compare to Other Promise Libs

FAQ

Unhandled Rejection

API

Utils

Observable

Unit Test

Benchmark

Contribute