node.js中等待任務完成

Question

所以我寫這Node.js的程序導入XML文件轉換成JSON對象的數組。我有2個文件導入，teachers.xml和students.xml。

教師和學生包含幾千有關教師和學生信息的。我用我的代碼覆蓋了這部分。

這是我的JavaScript文件解析文件：

var fs = require('fs'); 
var xmldom = require('xmldom'); 
var async = require('async'); 

// Parse `catalog` xml file and call `callback(catalog domxml root)` 
function parse_catalog(catalog, callback) { 
    // Read xml file content 
    fs.readFile(catalog, function (err, data) { 
     if (err) { 
      throw 'Error reading XML catalog'; 
     } else { 
      // Parse xml content and return dom root 
      var domRoot = new xmldom.DOMParser().parseFromString(data.toString()); 
      // Call callback passing dom root 
      callback(domRoot) 
    } 
}); 
} 

我有兩個方法，這樣對XML轉換成JSON和它的工作完美（一個教師，一個用於學生）

// Convert teacher XML into json format in a array 
function convert_teachers(domCatalog) { 
    var teachers = domCatalog.getElementsByTagName('teacher'); 
    var teachers_arr= []; 
    for (var i = 0; i < teachers .length; i++) { 
     var teacher= teachers[i]; 
     ... 
     //Reading the xml 

     teachers_arr.push({ 
     ... 
     //Create the json 

     }); 
    } 
    console.log("Teachers are now in JSON format "); 
} 

所以最終我必須做的是這樣的：

parse_catalog('teachers.xml', convert_teachers); 

當我這樣做：

parse_catalog('teachers.xml', convert_teachers); 
parse_catalog('students.xml', convert_students); 

一方或另一方將完成第一個因要素進口的數量，女巫是正常的，我認爲。

我要的是等待兩個需要進口，然後做一些JavaScript操作，這是我在哪裏卡住了。

我試着用異步做到這一點，但它不沒有等到這兩個文件完成導入。

async.parallel([ 
    function(callback) { 
     parse_catalog('teachers.xml', convert_teachers); 
     callback(); 
    }, 

    function(callback) { 
     parse_catalog('students.xml', convert_students); 
     callback(); 
    } 
], function(err) { 
    if (err) return next(err); 

    console.log("Finished"); 
    //Enventually some Javascript manipulations on the two arrays 

}); 

其實它輸出：

Finished 
Teachers are now in JSON format 
Students are now in JSON format 

，或者根據文件的大小

Finished 
Students are now in JSON format 
Teachers are now in JSON format 

我想更重要的是這樣的：

Teachers are now in JSON format (or students) 
Students are now in JSON format (or teachers) 
Finished 

我打算加載2個以上的文件，以及它們的順序加載對我無關緊要。

任何線索？謝謝！

Answer 1

您在async.parallel()函數中執行callback()的功能太快，因爲那時fs.readFile()還沒有開始。嘗試這樣的事情，而不是：

function parse_catalog(catalog, callback) { 
    // Read xml file content 
    fs.readFile(catalog, function(err, data) { 
    if (err) 
     return callback(err); 

    // Parse xml content and return dom root 
    var domRoot = new xmldom.DOMParser().parseFromString(data.toString()); 

    // Call callback passing dom root 
    callback(null, domRoot); 
    }); 
} 

// Convert teacher XML into json format in a array 
function convert_teachers(domCatalog) { 
    var teachers = domCatalog.getElementsByTagName('teacher'); 
    var teachers_arr = []; 
    for (var i = 0; i < teachers .length; i++) { 
    var teacher = teachers[i]; 
    ... 
    //Reading the xml 

    teachers_arr.push({ 
    ... 
    //Create the json 

    }); 
    } 
    console.log('Teachers are now in JSON format'); 
    return teachers_arr; 
} 
// and similarly for `convert_students` 

async.parallel({ 
    teachers: function(callback) { 
    parse_catalog('teachers.xml', function(err, domCatalog) { 
     if (err) 
     return callback(err); 
     var teachers = convert_teachers(domCatalog); 
     callback(null, teachers); 
    }); 
    }, 
    students: function(callback) { 
    parse_catalog('students.xml', function(err, domCatalog) { 
     if (err) 
     return callback(err); 
     var students = convert_students(domCatalog); 
     callback(null, students); 
    }); 
    } 
}, function(err, results) { 
    if (err) return next(err); 

    console.log('Finished'); 

    // here you have `results.teachers` and `results.students` 
    console.dir(results); 
});