# 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~
资源推荐
资源详情
资源评论
收起资源包目录
node.js之express的token验证 (467个子文件)
range.bnf 619B
changelog 1KB
semver.cmd 182B
mime.cmd 170B
CODEOWNERS 11B
style.css 111B
.editorconfig 399B
index.ejs 222B
error.ejs 83B
.eslintignore 5B
.eslintrc 554B
.eslintrc 348B
.eslintrc 180B
express之token验证用户身份信息.iml 469B
Jakefile 2KB
ejs.js 42KB
async.js 38KB
async.js 38KB
semver.js 37KB
sbcs-data-generated.js 31KB
response.js 26KB
ejs.js 25KB
index.js 25KB
index.js 23KB
parse.js 22KB
dbcs-codec.js 21KB
ejs.min.js 20KB
stringify.js 20KB
qs.js 19KB
index.js 18KB
ipaddr.js 18KB
tests.js 15KB
index.js 15KB
application.js 14KB
async.min.js 12KB
request.js 12KB
jwt.test.js 11KB
index.js 10KB
index.js 10KB
index.js 10KB
ipaddr.min.js 9KB
utf7.js 9KB
extend-node.js 8KB
dbcs-data.js 8KB
index.js 7KB
verify.js 7KB
sign.js 7KB
index.js 6KB
index.js 6KB
stringify.js 6KB
internal.js 6KB
index.js 6KB
index.js 6KB
index.js 6KB
node.js 6KB
index.js 6KB
utils.js 6KB
unless.tests.js 6KB
parse.js 6KB
urlencoded.js 6KB
index.js 6KB
utils.js 5KB
index.js 5KB
mediaType.js 5KB
index.js 5KB
index.js 5KB
utf16.js 5KB
ecdsa-sig-formatter.js 5KB
json.js 5KB
index.js 5KB
browser.js 5KB
index.js 4KB
debug.js 4KB
sbcs-data.js 4KB
index.js 4KB
route.js 4KB
index.js 4KB
read.js 4KB
utils.js 4KB
index.js 4KB
index.js 4KB
index.js 4KB
encoding.js 3KB
language.js 3KB
index.js 3KB
index.js 3KB
streams.js 3KB
index.js 3KB
index.js 3KB
view.js 3KB
layer.js 3KB
verify-stream.js 3KB
charset.js 3KB
index.js 3KB
index.js 3KB
index.js 3KB
index.js 3KB
index.js 3KB
mime.js 3KB
index.js 3KB
共 467 条
- 1
- 2
- 3
- 4
- 5
资源评论
- 疯子蚁2021-03-10写得很详细,谢谢大佬
- 懒羊羊哇2020-12-130积分白嫖了,谢谢大佬
codeXml
- 粉丝: 86
- 资源: 2
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