javascript - node.js:如何在 forEach 循环中使用异步调用实现路由方法？

Question

我必须实现这样的逻辑:

var express = require('express'),
    request = require('request');

var array = [
  { url: 'http://www.example1.com' },
  { url: 'http://www.example2.com' },
];

express.Router().get('/job', function (req, res) {
  results = [];
  array.forEach(function (item) {
    request(item.url, function (error, response, body) {
      if (!error && response.statusCode == 200) {
        results.push(body);
      }
  });
  res.json(results); // <== wrong, results array is empty, here...
});

如何调用 res.json(results) 确保 forEach 循环结束？

更新:它不是建议答案的重复!

我需要在所有请求完成时执行 res.json()，而在 forEach 循环完成时不需要...:-(

Answer 1

实现此目的的简单方法:

var express = require('express'),
    request = require('request');

var array = [
  { url: 'http://www.example1.com' },
  { url: 'http://www.example2.com' },
];

//store number of completed calls
var completed = 0;

express.Router().get('/job', function (req, res) {
  results = [];
  array.forEach(function (item) {
    request(item.url, function (error, response, body) {
      if (!error && response.statusCode == 200) {
        results.push(body);

        completed = completed + 1; //iterate counter
        onComplete(); //attempt completion
      }
  });

  function onComplete(){
    if(completed != array.length) {
      return;
    }
    res.json(results); 
    // ... rest of code that relies on results
  };

});