node.js async.series是如何工作的？

Question

var async = require('async');

function callbackhandler(err, results) {
    console.log('It came back with this ' + results);
}   

function takes5Seconds(callback) {
    console.log('Starting 5 second task');
    setTimeout( function() { 
        console.log('Just finshed 5 seconds');
        callback(null, 'five');
    }, 5000);
}   

function takes2Seconds(callback) {
    console.log('Starting 2 second task');
    setTimeout( function() { 
        console.log('Just finshed 2 seconds');
        callback(null, 'two');
    }, 2000); 
}   

async.series([takes2Seconds(callbackhandler), 
              takes5Seconds(callbackhandler)], function(err, results){
    console.log('Result of the whole run is ' + results);
}) 

输出如下所示:

Starting 2 second task
Starting 5 second task
Just finshed 2 seconds
It came back with this two
Just finshed 5 seconds
It came back with this five

我期待take2Second函数在take5Second开始之前完全完成.它是如何工作的.请告诉我.而最终的功能永远不会运行.谢谢.

Answer 1

不完全的.您正在立即执行这些功能(一旦评估了数组),这就是它们似乎同时启动的原因.

传递给要执行的每个函数的回调是异步库的内部.一旦函数完成,执行它,传递错误和/或值.您不需要自己定义该功能.

最后的函数永远不会在你的情况下运行,因为async需要你调用以回到系列中的下一个函数的回调函数从未实际执行过(只有你的callbackHandler函数被执行).

试试这个:

async.series([
    takes2Seconds,
    takes5seconds
], function (err, results) {
    // Here, results is an array of the value from each function
    console.log(results); // outputs: ['two', 'five']
});

Answer 2

詹姆斯给了你很好的概述async.series.请注意,您可以在系列数组中设置匿名函数,然后使用参数调用实际函数

var async = require('async')
var param1 = 'foobar'
function withParams(param1, callback) {
  console.log('withParams function called')
  console.log(param1)
  callback()
}
function withoutParams(callback) {
  console.log('withoutParams function called')
  callback()
}
async.series([
  function(callback) {
    withParams(param1, callback)
  },
  withoutParams
], function(err) {
  console.log('all functions complete')
})

Answer 3

我创建异步系列的首选方法是使用操作数组,如下所示;

var async = require('async'),
    operations = [];

operations.push(takes2Seconds);
operations.push(takes5seconds);

async.series(operations, function (err, results) {
    // results[1]
    // results[2]
});

function takes2Seconds(callback) {
    callback(null, results);
}

function takes5seconds(callback) {
    callback(null, results);
}

Answer 4

async.series
    ([  
        function (callback)
        {
            response=wsCall.post(user,url,method,response);
            console.log("one");
            callback();
        }
        ,
        function (callback)
        {
            console.log("two");
            //console.log(response);
            callback();
        }
    ]
    ,
    function(err) 
    {
        console.log('Both a and b are saved now');
        console.log(response);
    });