node.js等待任务完成

node.js Wait for task to be finished

本文关键字：任务 等待 js node      更新时间：2023-09-26

所以我正在编写这个node.js程序，将XML文件导入JSON对象数组。我有两个文件要导入，teachers.xml和students.xml。

《教师和学生》包含了数千条关于教师和学生的信息。我的代码很好地涵盖了这一部分。

这是我解析文件的javascript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)
    }
});
}

我有两种类似的方法可以将xml转换为json，并且它可以完美地工作（一种用于教师，一种用于学生）

// 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 ");
}

所以最后我要做的就是：

parse_catalog('teachers.xml', convert_teachers);

当我这样做时：

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

根据要导入的元素数量，其中一个或另一个将首先完成，我认为这很正常。

我想要的是等待两者都被导入，然后进行一些javascript操作，这就是我的困境。

我试着用async来做这件事，但它不会等到两个文件完成后再导入。

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
});

实际上它输出：

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

或取决于文件大小

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

我想要的更像是：

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

我计划再加载2个文件，加载顺序对我来说无关紧要。

有线索吗？谢谢

您在async.parallel()函数中执行callback()太早了，因为到那时fs.readFile()还没有启动。试试这样的东西：

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);
});
相关文章：