欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  IT编程

js001 ---- async

程序员文章站 2023-12-13 21:35:10
Node.js异步流,详细见https://caolan.github.io/async/docs.html#parallel 1, async 用的比较多的是 waterfall, 瀑布流, 就是每个异步函数按照顺序执行。如果出错了,可以callback(new Error("xxxx"), Co ......

node.js异步流,详细见https://caolan.github.io/async/docs.html#parallel

1, async 

用的比较多的是 waterfall, 瀑布流, 就是每个异步函数按照顺序执行。如果出错了,可以callback(new error("xxxx"), code.fail);

async 最好用的流程控制方法, 可大大降低代码耦合度。 (一个函数只做一件事, async.waterfall则实现了一序列函数的异步组合)

async.waterfall([
    function(callback) {
        callback(null, 'one', 'two');
    },
    function(arg1, arg2, callback) {
        // arg1 now equals 'one' and arg2 now equals 'two'
        callback(null, 'three');
    },
    function(arg1, callback) {
        // arg1 now equals 'three'
        callback(null, 'done');
    }
], function (err, result) {
    // result now equals 'done'
});

// or, with named functions:
async.waterfall([
    myfirstfunction,
    mysecondfunction,
    mylastfunction,
], function (err, result) {
    // result now equals 'done'
});
function myfirstfunction(callback) {
    callback(null, 'one', 'two');
}
function mysecondfunction(arg1, arg2, callback) {
    // arg1 now equals 'one' and arg2 now equals 'two'
    callback(null, 'three');
}
function mylastfunction(arg1, callback) {
    // arg1 now equals 'three'
    callback(null, 'done');
}

 

parallel async.parallel(tasks, callback)

tasks 并行运行函数集合, 而不必等到上一个函数完成, 如果任何函数发送错误, 会立刻执行回调函数,并返回错误信息; 若没有发生错误, 则会在所有tasks函数执行完毕之后用回调函数将结果返回。

async.parallel([
    function(callback) {
        settimeout(function() {
            callback(null, 'one');
        }, 200);
    },
    function(callback) {
        settimeout(function() {
            callback(null, 'two');
        }, 100);
    }
],
// optional callback
function(err, results) {
    // the results array will equal ['one','two'] even though
    // the second function had a shorter timeout.
});

// an example using an object instead of an array
async.parallel({
    one: function(callback) {
        settimeout(function() {
            callback(null, 1);
        }, 200);
    },
    two: function(callback) {
        settimeout(function() {
            callback(null, 2);
        }, 100);
    }
}, function(err, results) {
    // results is now equals to: {one: 1, two: 2}
});

eachseries(coll, iteratee, callbackopt)       跟each一样,不过 一次只运行一个异步操作,       the same as  but runs only a single async operation at a time.

map 跟each 类似。

// assuming openfiles is an array of file names and savefile is a function
// to save the modified contents of that file:

async.each(openfiles, savefile, function(err){
  // if any of the saves produced an error, err would equal that error
});

// assuming openfiles is an array of file names
async.each(openfiles, function(file, callback) {

    // perform operation on file here.
    console.log('processing file ' + file);

    if( file.length > 32 ) {
      console.log('this file name is too long');
      callback('file name too long');
    } else {
      // do work to process file here
      console.log('file processed');
      callback();
    }
}, function(err) {
    // if any of the file processing produced an error, err would equal that error
    if( err ) {
      // one of the iterations produced an error.
      // all processing will now stop.
      console.log('a file failed to process');
    } else {
      console.log('all files have been processed successfully');
    }
});

 

————————————————————————————————————————————————————————————

以上就是node.js async 的主要知识。

上一篇:

下一篇: