nodejs：async.series 未按顺序执行函数

Question

在以下代码中，async.series 块没有按顺序执行。

var fs = require("fs");
var async = require("async");
var buffer = new Buffer(10);
var read = "";
var readByt;
async.series([
    function(callback) {
        console.log("test");
        callback();
    },
    function(callback) {
        fs.open('c:/ab.txt', 'r+', function(err, fd) {
            fs.read(fd, buffer, 0, buffer.length, 0, function(err, bytes){
                read = buffer.slice(0, bytes).toString();
                readByt = bytes;        
                console.log("}}}"+read);
                fs.close(fd, function(err){
                    if (err){
                    console.log(err);
                    } 
                    console.log("File closed successfully.");           
                })
            })
        })
        callback();
    },
    function (callback){
        console.log("console:"+read);
        console.log("console:"+read.substr(read.length-1));
        console.log("console:"+buffer.slice(0, readByt).toString());
        callback();
    }
],function(){});

通过命令行执行时，第三个块中的缓冲区打印发生在文件读取操作之前。

c:\>node fr.js
test
console:
console:
console: ?F     p?
}}}c:/log.txt
File closed successfully.

如何让这些按顺序执行？

Answer 1

您的回调将在每个异步函数完成后调用。在您的情况下， fs 操作是异步的，并在以后完成。在 fs 操作完成之前，回调将被调用。

试试这个，在 fs.close 中调用回调。

var fs = require("fs");
var async = require("async");
var buffer = new Buffer(10);
var read = "";
var readByt;
async.series([
    function(callback) {
        console.log("test");
        callback();
    },
    function(callback) {
        fs.open('c:/ab.txt', 'r+', function(err, fd) {
            fs.read(fd, buffer, 0, buffer.length, 0, function(err, bytes){
                read = buffer.slice(0, bytes).toString();
                readByt = bytes;        
                console.log("}}}"+read);
                fs.close(fd, function(err){
                    if (err){
                    console.log(err);
                    } 
                    console.log("File closed successfully."); 
                    callback();          
                })
            })
        })
    },
    function (callback){
        console.log("console:"+read);
        console.log("console:"+read.substr(read.length-1));
        console.log("console:"+buffer.slice(0, readByt).toString());
        callback();
    }
],function(){});