Javascript async异步操作库简介
异步操作知识
在js世界中, 异步操作非常流行, nodejs就是特点基于异步非阻塞。
js语言支持的异步语法包括, Promise async await generator yield。
这些语法需要使用者了解非常清楚, 往往很困难。
下面介绍一个异步操作的超级库,可以实现很多异步操作和流程控制。
async库
http://caolan.github.io/async/index.html
Async is a utility module which provides straight-forward, powerful functions for working with asynchronous JavaScript. Although originally designed for use with Node.js and installable via
npm install --save async
, it can also be used directly in the browser.
浏览器也可以用!!!
Async provides around 70 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 asynchronous function -- a callback which expects an Error as its first argument -- and calling the callback once.
包括70个异步函数, 包括 函数类型的 map reduce filter
以及 异步控制流函数 parallel series
DEMO
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'], function(filePath, callback) { fs.access(filePath, function(err) { callback(null, !err) }); }, function(err, results) { // results now equals an array of the existing files }); async.parallel([ function(callback) { ... }, function(callback) { ... } ], function(err, results) { // optional callback }); async.series([ function(callback) { ... }, function(callback) { ... } ]);
parallel 并行执行,效率高。 === Promise.all
series 按照前后顺序执行。
race 竞态执行。 === Promise.race