javascript - 如何从 Node 中的函数返回数据？

Question

我正在使用 Express 并尝试自学 Node/javascript 回调，但我偶然发现了一些东西。

我有一条如下所示的路线:

var express = require('express');
var router = express.Router();
var api = require('../api');

router.get('/',function(req, res, next){
  var modulename = api.modulename;
  modulename.methodname(res);
});

module.exports = router;

然后上面调用的模块如下所示:

var library = require('library');
var instances = {};
var modulename = {

  getAllInstances: function(res) {
    var request = new library.asyncMethod();
    request.on('success', function(resp) {
      instances = resp.data; 
      res.setHeader("Content-Type","application/json");
      var returnInstances = {
        id: instances[0].InstanceId,
        state: {name: instances[0].State.Name, code: instances[0].State.Code}
      };
      res.send(returnInstances);
    })
    .on('error', function(resp){
      console.log(resp);
    })
  }
};

module.exports = modulename;

如您所见，我正在将响应参数传递到我的模块，但我宁愿传回实例，然后在路由中返回api.modulename.instances，像这样:

var library = require('library');
var instances = {};
var modulename = {

  getAllInstances: function() {
    var request = new library.asyncMethod();
    request.on('success', function(resp) {
      var returnData = resp.data;
      instances = {
        id: returnData[0].InstanceId,
        state: {name: returnData[0].State.Name, code: returnData[0].State.Code}
      };
    })
    .on('error', function(resp){
      console.log(resp);
    })
    .send();
  }
};

module.exports = modulename;

但是，当我这样做时，它会作为默认值 {} 出现，但如果我按照上面的方式运行它，我会得到输出，所以我知道其中应该有数据。

Answer 1

如果我误解了您的问题，请告诉我。如果您说要从 getAllInstances 传回对象，那么您可以传入一个回调并从事件处理程序中调用它，如下所示 -

router.get('/',function(req, res, next){
  var modulename = api.modulename;
  modulename.getAllInstances(res, function(err, instances){
     if(err){  ... }
     else{
        res.send(instances);    //or however you want to use instances
     }
  });
});

和getInstances

var modulename = {
  getAllInstances: function(res, cb) {
    var request = new library.asyncMethod();
    request.on('success', function(resp) {
      instances = resp.data; 

      var returnInstances = {
        id: instances[0].InstanceId,
        state: {name: instances[0].State.Name, code: instances[0].State.Code}
      };
      cb(null, instances);
    })
    .on('error', function(err){
      cb(err, null));
    });
    //.send();    not sure what this is it seems to be request.send()  ??
  }
};