Question

我有一个方法，我想在执行回调之前做一些请求和计算。我发现很多人建议使用async模块但是在调用回调之前它仍然没有等待回调完成。这是我想要完成的示例代码。

loop.js

var ex_obj = require('./ex_obj');
var array2loop = [
  arr1 = new ex_obj(),
  arr2 = new ex_obj(),
  arr3 = new ex_obj()
];

var loop = function(){
  for(var i=0; i < array2loop.length; i++){
    array2loop[i].incrementNumber(function log(){
      console.log('Should fire last: ' + array2loop[i].number);
    });
  }
  setTimeout(loop, 5000);
};

loop();

ex_obj.js

var async = require('async');
var ex_obj = function(){
  var self = this;
  self.number = 0;
  self.incrementNumber = function(callback){
    self.number = ++self.number;
    // This setTimeout is a placeholder for a url request
    // that I don't know how long will take.
    setTimeout(function(){
      console.log('Should fire first: '+self.number);
    }, 2000);
    callback();
  };
};
module.exports = ex_obj;

按原样运行时，我会得到以下内容

Should fire last: 1
Should fire last: 1
Should fire last: 1
Should fire first: 1
Should fire first: 1
Should fire first: 1
Should fire last: 2
...etc

如果我进行了以下更改，我会收到“无法读取未定义的属性”编号错误：

ex_obj.js

  self.incrementNumber = function(callback){
    self.number = ++self.number;
    setTimeout(function(){
      console.log('Should fire first: '+self.number);
      callback();
    }, 2000);
  };

所以我尝试使用async.series仅在超时运行后调用回调

ex_obj.js

async.series([
  function(){
    setTimeout(function(){
      console.log('Should fire first '+self.number);
    }, 2000)}],
  callback()
);

这仍然导致上面的输出。我知道这是一个常见问题，但我似乎无法找到解决回调内部回调的解决方案。感谢您提供任何帮助！

Answer 1

我猜你需要这样的东西：

var ex_obj = function () {
  var self = this;
  self.number = 0;
  self.incrementNumber = function (callback) {
    self.number = ++self.number;
    setTimeout(callback, 2000);
    console.log('Should fire first: ' + self.number);
  };
};

var array2loop = [
  arr1 = new ex_obj(),
  arr2 = new ex_obj(),
  arr3 = new ex_obj()
];

var loop = function () {
  array2loop.forEach(function (element) {
    element.incrementNumber(function () {
      console.log('Should fire last: ' + element.number);
    });
  });
  setTimeout(loop, 5000);
};

loop();

输出：

Should fire first: 1
Should fire first: 1
Should fire first: 1
Should fire last: 1
Should fire last: 1
Should fire last: 1
Should fire first: 2
Should fire first: 2
Should fire first: 2
Should fire last: 2
Should fire last: 2
Should fire last: 2
...

在另一个函数的回调完成后调用callback（）

1 个答案: