# Async.js
[![Build Status via Travis CI](https://travis-ci.org/caolan/async.svg?branch=master)](https://travis-ci.org/caolan/async)
[![NPM version](http://img.shields.io/npm/v/async.svg)](https://www.npmjs.org/package/async)
[![Coverage Status](https://coveralls.io/repos/caolan/async/badge.svg?branch=master)](https://coveralls.io/r/caolan/async?branch=master)
[![Join the chat at https://gitter.im/caolan/async](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/caolan/async?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
Async is a utility module which provides straight-forward, powerful functions
for working with asynchronous JavaScript. Although originally designed for
use with [Node.js](http://nodejs.org) and installable via `npm install async`,
it can also be used directly in the browser.
Async is also installable via:
- [bower](http://bower.io/): `bower install async`
- [component](https://github.com/component/component): `component install
caolan/async`
- [jam](http://jamjs.org/): `jam install async`
- [spm](http://spmjs.io/): `spm install async`
Async provides around 20 functions that include the usual 'functional'
suspects (`map`, `reduce`, `filter`, `each`…) as well as some common patterns
for asynchronous control flow (`parallel`, `series`, `waterfall`…). All these
functions assume you follow the Node.js convention of providing a single
callback as the last argument of your `async` function.
## Quick Examples
```javascript
async.map(['file1','file2','file3'], fs.stat, function(err, results){
// results is now an array of stats for each file
});
async.filter(['file1','file2','file3'], fs.exists, function(results){
// results now equals an array of the existing files
});
async.parallel([
function(){ ... },
function(){ ... }
], callback);
async.series([
function(){ ... },
function(){ ... }
]);
```
There are many more functions available so take a look at the docs below for a
full list. This module aims to be comprehensive, so if you feel anything is
missing please create a GitHub issue for it.
## Common Pitfalls <sub>[(StackOverflow)](http://stackoverflow.com/questions/tagged/async.js)</sub>
### Synchronous iteration functions
If you get an error like `RangeError: Maximum call stack size exceeded.` or other stack overflow issues when using async, you are likely using a synchronous iterator. By *synchronous* we mean a function that calls its callback on the same tick in the javascript event loop, without doing any I/O or using any timers. Calling many callbacks iteratively will quickly overflow the stack. If you run into this issue, just defer your callback with `async.setImmediate` to start a new call stack on the next tick of the event loop.
This can also arise by accident if you callback early in certain cases:
```js
async.eachSeries(hugeArray, function iterator(item, callback) {
if (inCache(item)) {
callback(null, cache[item]); // if many items are cached, you'll overflow
} else {
doSomeIO(item, callback);
}
}, function done() {
//...
});
```
Just change it to:
```js
async.eachSeries(hugeArray, function iterator(item, callback) {
if (inCache(item)) {
async.setImmediate(function () {
callback(null, cache[item]);
});
} else {
doSomeIO(item, callback);
//...
```
Async guards against synchronous functions in some, but not all, cases. If you are still running into stack overflows, you can defer as suggested above, or wrap functions with [`async.ensureAsync`](#ensureAsync) Functions that are asynchronous by their nature do not have this problem and don't need the extra callback deferral.
If JavaScript's event loop is still a bit nebulous, check out [this article](http://blog.carbonfive.com/2013/10/27/the-javascript-event-loop-explained/) or [this talk](http://2014.jsconf.eu/speakers/philip-roberts-what-the-heck-is-the-event-loop-anyway.html) for more detailed information about how it works.
### Multiple callbacks
Make sure to always `return` when calling a callback early, otherwise you will cause multiple callbacks and unpredictable behavior in many cases.
```js
async.waterfall([
function (callback) {
getSomething(options, function (err, result) {
if (err) {
callback(new Error("failed getting something:" + err.message));
// we should return here
}
// since we did not return, this callback still will be called and
// `processData` will be called twice
callback(null, result);
});
},
processData
], done)
```
It is always good practice to `return callback(err, result)` whenever a callback call is not the last statement of a function.
### Binding a context to an iterator
This section is really about `bind`, not about `async`. If you are wondering how to
make `async` execute your iterators in a given context, or are confused as to why
a method of another library isn't working as an iterator, study this example:
```js
// Here is a simple object with an (unnecessarily roundabout) squaring method
var AsyncSquaringLibrary = {
squareExponent: 2,
square: function(number, callback){
var result = Math.pow(number, this.squareExponent);
setTimeout(function(){
callback(null, result);
}, 200);
}
};
async.map([1, 2, 3], AsyncSquaringLibrary.square, function(err, result){
// result is [NaN, NaN, NaN]
// This fails because the `this.squareExponent` expression in the square
// function is not evaluated in the context of AsyncSquaringLibrary, and is
// therefore undefined.
});
async.map([1, 2, 3], AsyncSquaringLibrary.square.bind(AsyncSquaringLibrary), function(err, result){
// result is [1, 4, 9]
// With the help of bind we can attach a context to the iterator before
// passing it to async. Now the square function will be executed in its
// 'home' AsyncSquaringLibrary context and the value of `this.squareExponent`
// will be as expected.
});
```
## Download
The source is available for download from
[GitHub](https://github.com/caolan/async/blob/master/lib/async.js).
Alternatively, you can install using Node Package Manager (`npm`):
npm install async
As well as using Bower:
bower install async
__Development:__ [async.js](https://github.com/caolan/async/raw/master/lib/async.js) - 29.6kb Uncompressed
## In the Browser
So far it's been tested in IE6, IE7, IE8, FF3.6 and Chrome 5.
Usage:
```html
<script type="text/javascript" src="async.js"></script>
<script type="text/javascript">
async.map(data, asyncProcess, function(err, results){
alert(results);
});
</script>
```
## Documentation
Some functions are also available in the following forms:
* `<name>Series` - the same as `<name>` but runs only a single async operation at a time
* `<name>Limit` - the same as `<name>` but runs a maximum of `limit` async operations at a time
### Collections
* [`each`](#each), `eachSeries`, `eachLimit`
* [`forEachOf`](#forEachOf), `forEachOfSeries`, `forEachOfLimit`
* [`map`](#map), `mapSeries`, `mapLimit`
* [`filter`](#filter), `filterSeries`, `filterLimit`
* [`reject`](#reject), `rejectSeries`, `rejectLimit`
* [`reduce`](#reduce), [`reduceRight`](#reduceRight)
* [`detect`](#detect), `detectSeries`, `detectLimit`
* [`sortBy`](#sortBy)
* [`some`](#some), `someLimit`
* [`every`](#every), `everyLimit`
* [`concat`](#concat), `concatSeries`
### Control Flow
* [`series`](#seriestasks-callback)
* [`parallel`](#parallel), `parallelLimit`
* [`whilst`](#whilst), [`doWhilst`](#doWhilst)
* [`until`](#until), [`doUntil`](#doUntil)
* [`during`](#during), [`doDuring`](#doDuring)
* [`forever`](#forever)
* [`waterfall`](#waterfall)
* [`compose`](#compose)
* [`seq`](#seq)
* [`applyEach`](#applyEach), `applyEachSeries`
* [`queue`](#queue), [`priorityQueue`](#priorityQueue)
* [`cargo`](#cargo)
* [`auto`](#auto)
* [`retry`](#retry)
* [`iterator`](#iterator)
* [`times`](#times), `timesSeri
没有合适的资源?快使用搜索试试~ 我知道了~
温馨提示
【项目资源】: 包含前端、后端、移动开发、操作系统、人工智能、物联网、信息化管理、数据库、硬件开发、大数据、课程资源、音视频、网站开发等各种技术项目的源码。 包括STM32、ESP8266、PHP、QT、Linux、iOS、C++、Java、python、web、C#、EDA、proteus、RTOS等项目的源码。 【项目质量】: 所有源码都经过严格测试,可以直接运行。 功能在确认正常工作后才上传。 【适用人群】: 适用于希望学习不同技术领域的小白或进阶学习者。 可作为毕设项目、课程设计、大作业、工程实训或初期项目立项。 【附加价值】: 项目具有较高的学习借鉴价值,也可直接拿来修改复刻。 对于有一定基础或热衷于研究的人来说,可以在这些基础代码上进行修改和扩展,实现其他功能。 【沟通交流】: 有任何使用上的问题,欢迎随时与博主沟通,博主会及时解答。 鼓励下载和使用,并欢迎大家互相学习,共同进步。
资源推荐
资源详情
资源评论
收起资源包目录
毕设&课设&项目&实训-基于Webpack和Vue的前端工程化实践.zip (2000个子文件)
benchmark-native.c 613B
style.css 602B
style.css 152B
index.html 2KB
error.html 276B
example.html 200B
index.html 6B
lodash.js 526KB
lodash.min.js 71KB
index.js 66KB
browser.js 59KB
server.js 50KB
index.js 41KB
parser.js 38KB
dashdash.js 34KB
semver.js 32KB
sbcs-data-generated.js 31KB
uri.js 29KB
_stream_readable.js 28KB
browser.js 27KB
response.js 25KB
index.js 24KB
index.js 24KB
plural.js 22KB
index.js 21KB
dbcs-codec.js 21KB
cors.js 18KB
parse.js 18KB
server.js 18KB
parse.js 18KB
client.js 17KB
index.js 17KB
_baseConvert.js 16KB
_stream_writable.js 16KB
ipaddr.js 15KB
index.js 15KB
punycode.js 14KB
index.js 14KB
document.js 14KB
application.js 14KB
signer.js 13KB
request.js 12KB
pkcs8.js 12KB
auth-token.test.js 11KB
x509.js 11KB
unicode.js 11KB
unicode.js 11KB
stringify.js 11KB
validate.js 11KB
misc.js 10KB
client.js 10KB
client.js 10KB
aws4.js 10KB
_mapping.js 10KB
index.js 10KB
parser.js 10KB
utf7.js 9KB
template.js 9KB
polyfills.js 9KB
extend-node.js 8KB
dhe.js 8KB
certificate.js 8KB
dbcs-data.js 8KB
index.js 8KB
pkcs1.js 8KB
plural.js 7KB
stringify_test.js 7KB
parse.js 7KB
ipaddr.min.js 7KB
openssh-cert.js 7KB
index.js 7KB
key.js 7KB
index.js 7KB
utils.js 7KB
wrapperLodash.js 7KB
run.js 7KB
graceful-fs.js 7KB
ssh-private.js 7KB
index.js 7KB
identity.js 7KB
index.js 6KB
_stream_transform.js 6KB
signature.js 6KB
internal.js 6KB
private-key.js 6KB
debounce.js 6KB
index.js 6KB
index.js 6KB
utils.js 6KB
urlencoded.js 6KB
index.js 5KB
index.js 5KB
assert.js 5KB
assert.js 5KB
uuid.js 5KB
node.js 5KB
utf16.js 5KB
algs.js 5KB
body-events.js 5KB
pem.js 5KB
共 2000 条
- 1
- 2
- 3
- 4
- 5
- 6
- 20
资源评论
妄北y
- 粉丝: 0
- 资源: 1万+
上传资源 快速赚钱
- 我的内容管理 展开
- 我的资源 快来上传第一个资源
- 我的收益 登录查看自己的收益
- 我的积分 登录查看自己的积分
- 我的C币 登录后查看C币余额
- 我的收藏
- 我的下载
- 下载帮助
安全验证
文档复制为VIP权益,开通VIP直接复制
信息提交成功