[![Build Status](https://secure.travis-ci.org/kriskowal/q.png?branch=master)](http://travis-ci.org/kriskowal/q)
<a href="http://promises-aplus.github.com/promises-spec">
<img src="http://promises-aplus.github.com/promises-spec/assets/logo-small.png"
align="right" alt="Promises/A+ logo" />
</a>
If a function cannot return a value or throw an exception without
blocking, it can return a promise instead. A promise is an object
that represents the return value or the thrown exception that the
function may eventually provide. A promise can also be used as a
proxy for a [remote object][Q-Connection] to overcome latency.
[Q-Connection]: https://github.com/kriskowal/q-connection
On the first pass, promises can mitigate the “[Pyramid of
Doom][POD]”: the situation where code marches to the right faster
than it marches forward.
[POD]: http://calculist.org/blog/2011/12/14/why-coroutines-wont-work-on-the-web/
```javascript
step1(function (value1) {
step2(value1, function(value2) {
step3(value2, function(value3) {
step4(value3, function(value4) {
// Do something with value4
});
});
});
});
```
With a promise library, you can flatten the pyramid.
```javascript
Q.fcall(promisedStep1)
.then(promisedStep2)
.then(promisedStep3)
.then(promisedStep4)
.then(function (value4) {
// Do something with value4
})
.catch(function (error) {
// Handle any error from all above steps
})
.done();
```
With this approach, you also get implicit error propagation, just like `try`,
`catch`, and `finally`. An error in `promisedStep1` will flow all the way to
the `catch` function, where it’s caught and handled. (Here `promisedStepN` is
a version of `stepN` that returns a promise.)
The callback approach is called an “inversion of control”.
A function that accepts a callback instead of a return value
is saying, “Don’t call me, I’ll call you.”. Promises
[un-invert][IOC] the inversion, cleanly separating the input
arguments from control flow arguments. This simplifies the
use and creation of API’s, particularly variadic,
rest and spread arguments.
[IOC]: http://www.slideshare.net/domenicdenicola/callbacks-promises-and-coroutines-oh-my-the-evolution-of-asynchronicity-in-javascript
## Getting Started
The Q module can be loaded as:
- A ``<script>`` tag (creating a ``Q`` global variable): ~2.5 KB minified and
gzipped.
- A Node.js and CommonJS module, available in [npm](https://npmjs.org/) as
the [q](https://npmjs.org/package/q) package
- An AMD module
- A [component](https://github.com/component/component) as ``microjs/q``
- Using [bower](http://bower.io/) as ``q``
- Using [NuGet](http://nuget.org/) as [Q](https://nuget.org/packages/q)
Q can exchange promises with jQuery, Dojo, When.js, WinJS, and more.
## Resources
Our [wiki][] contains a number of useful resources, including:
- A method-by-method [Q API reference][reference].
- A growing [examples gallery][examples], showing how Q can be used to make
everything better. From XHR to database access to accessing the Flickr API,
Q is there for you.
- There are many libraries that produce and consume Q promises for everything
from file system/database access or RPC to templating. For a list of some of
the more popular ones, see [Libraries][].
- If you want materials that introduce the promise concept generally, and the
below tutorial isn't doing it for you, check out our collection of
[presentations, blog posts, and podcasts][resources].
- A guide for those [coming from jQuery's `$.Deferred`][jquery].
We'd also love to have you join the Q-Continuum [mailing list][].
[wiki]: https://github.com/kriskowal/q/wiki
[reference]: https://github.com/kriskowal/q/wiki/API-Reference
[examples]: https://github.com/kriskowal/q/wiki/Examples-Gallery
[Libraries]: https://github.com/kriskowal/q/wiki/Libraries
[resources]: https://github.com/kriskowal/q/wiki/General-Promise-Resources
[jquery]: https://github.com/kriskowal/q/wiki/Coming-from-jQuery
[mailing list]: https://groups.google.com/forum/#!forum/q-continuum
## Tutorial
Promises have a ``then`` method, which you can use to get the eventual
return value (fulfillment) or thrown exception (rejection).
```javascript
promiseMeSomething()
.then(function (value) {
}, function (reason) {
});
```
If ``promiseMeSomething`` returns a promise that gets fulfilled later
with a return value, the first function (the fulfillment handler) will be
called with the value. However, if the ``promiseMeSomething`` function
gets rejected later by a thrown exception, the second function (the
rejection handler) will be called with the exception.
Note that resolution of a promise is always asynchronous: that is, the
fulfillment or rejection handler will always be called in the next turn of the
event loop (i.e. `process.nextTick` in Node). This gives you a nice
guarantee when mentally tracing the flow of your code, namely that
``then`` will always return before either handler is executed.
In this tutorial, we begin with how to consume and work with promises. We'll
talk about how to create them, and thus create functions like
`promiseMeSomething` that return promises, [below](#the-beginning).
### Propagation
The ``then`` method returns a promise, which in this example, I’m
assigning to ``outputPromise``.
```javascript
var outputPromise = getInputPromise()
.then(function (input) {
}, function (reason) {
});
```
The ``outputPromise`` variable becomes a new promise for the return
value of either handler. Since a function can only either return a
value or throw an exception, only one handler will ever be called and it
will be responsible for resolving ``outputPromise``.
- If you return a value in a handler, ``outputPromise`` will get
fulfilled.
- If you throw an exception in a handler, ``outputPromise`` will get
rejected.
- If you return a **promise** in a handler, ``outputPromise`` will
“become” that promise. Being able to become a new promise is useful
for managing delays, combining results, or recovering from errors.
If the ``getInputPromise()`` promise gets rejected and you omit the
rejection handler, the **error** will go to ``outputPromise``:
```javascript
var outputPromise = getInputPromise()
.then(function (value) {
});
```
If the input promise gets fulfilled and you omit the fulfillment handler, the
**value** will go to ``outputPromise``:
```javascript
var outputPromise = getInputPromise()
.then(null, function (error) {
});
```
Q promises provide a ``fail`` shorthand for ``then`` when you are only
interested in handling the error:
```javascript
var outputPromise = getInputPromise()
.fail(function (error) {
});
```
If you are writing JavaScript for modern engines only or using
CoffeeScript, you may use `catch` instead of `fail`.
Promises also have a ``fin`` function that is like a ``finally`` clause.
The final handler gets called, with no arguments, when the promise
returned by ``getInputPromise()`` either returns a value or throws an
error. The value returned or error thrown by ``getInputPromise()``
passes directly to ``outputPromise`` unless the final handler fails, and
may be delayed if the final handler returns a promise.
```javascript
var outputPromise = getInputPromise()
.fin(function () {
// close files, database connections, stop servers, conclude tests
});
```
- If the handler returns a value, the value is ignored
- If the handler throws an error, the error passes to ``outputPromise``
- If the handler returns a promise, ``outputPromise`` gets postponed. The
eventual value or error has the same effect as an immediate return
value or thrown error: a value would be ignored, an error would be
forwarded.
If you are writing JavaScript for modern engines only or using
CoffeeScript, you may use `finally` instead of `fin`.
### Chaining
There are two ways to chain promises. You can chain promises
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Cordova添加自定义插件Demo
共238个文件
js:65个
java:43个
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Cordova添加自定义插件Demo (238个子文件)
android_sdk_version 1KB
resources.ap_ 1.69MB
MainActivity.apk 1.74MB
MyCordova.apk 1.74MB
gradlew.bat 2KB
list-started-emulators.bat 1KB
list-emulator-images.bat 1KB
install-emulator.bat 1KB
install-device.bat 1KB
start-emulator.bat 1KB
list-devices.bat 1KB
check_reqs.bat 1021B
version.bat 1015B
build.bat 1010B
clean.bat 1010B
log.bat 1006B
run.bat 1006B
build 1KB
check_reqs 1KB
WhitelistPlugin.class 3KB
MyIntentPlugin.class 3KB
WhitelistPlugin$CustomConfigXmlParser.class 3KB
MyPlugin.class 1KB
DemoActivity$1.class 1KB
SplashActivity.class 1KB
DemoActivity.class 932B
SplashActivity$1.class 814B
MainActivity.class 563B
R.class 503B
R$string.class 445B
R$id.class 427B
R$layout.class 415B
R$drawable.class 403B
R$xml.class 360B
BuildConfig.class 327B
R$attr.class 313B
.classpath 475B
clean 1KB
index.css 4KB
classes.dex 136KB
.gitignore 172B
build.gradle 11KB
cordova.gradle 7KB
plugin-build.gradle 2KB
build.gradle 2KB
settings.gradle 66B
gradlew 5KB
index.html 1KB
MainActivity.iml 709B
install-device 1KB
install-emulator 1KB
gradle-wrapper.jar 52KB
cordovalib-a9fa37da4df980f46ae0a44f88fa75ad.jar 48KB
CordovaWebViewImpl.java 21KB
NativeToJsMessageQueue.java 19KB
CordovaResourceApi.java 18KB
PluginManager.java 18KB
CordovaActivity.java 17KB
SystemWebViewClient.java 14KB
CordovaPlugin.java 13KB
SystemWebViewEngine.java 12KB
CoreAndroid.java 12KB
SystemWebChromeClient.java 11KB
CordovaBridge.java 7KB
Whitelist.java 7KB
PluginResult.java 6KB
WhitelistPlugin.java 6KB
CordovaDialogsHelper.java 6KB
LOG.java 6KB
CordovaInterfaceImpl.java 6KB
ConfigXmlParser.java 5KB
CallbackContext.java 5KB
CordovaWebView.java 5KB
CordovaArgs.java 3KB
CordovaPreferences.java 3KB
SystemWebView.java 3KB
CordovaWebViewEngine.java 3KB
MyIntentPlugin.java 3KB
CordovaClientCertRequest.java 3KB
CordovaInterface.java 2KB
PluginEntry.java 2KB
Config.java 2KB
ICordovaClientCertRequest.java 2KB
SystemExposedJsApi.java 2KB
SystemCookieManager.java 2KB
AuthenticationToken.java 2KB
CordovaHttpAuthHandler.java 2KB
ICordovaHttpAuthHandler.java 1KB
ExposedJsApi.java 1KB
MainActivity.java 1KB
ICordovaCookieManager.java 1KB
R.java 1KB
SplashActivity.java 874B
DemoActivity.java 839B
MyPlugin.java 779B
BuildConfig.java 151B
cordova.js 63KB
cordova.js 63KB
q.js 58KB
build.js 28KB
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