how to return response to REST api in node js

Question

I'm new to Node JS. My node js REST api route code is:

'use strict';
module.exports = function(app) {
    var sequel = require('../controllers/sampleController');
    app.get('/task?:email', function(req, res){
        res.send(sequel.listByEmail(req.query.email));
    });
};

And my listByEmail function is:

'use strict';
var apiKey = '1xxxxxxxxL';
exports.listByEmail = function(emailid) {
    console.log(emailid);
    if(emailid != null && emailid != undefined) {
        var xyz = require("xyz-api")(apiKey);
        xyz.person.findByEmail(emailid, function(err, data) {
            if(data.status == 200){
                return data; // data is in json format
            }
        });
    }
};

I returned data like this from that listbyemail function. Data is there, if i try to print the data in console it appears. But while returning the data, it won't returned. It's always return undefined. I can't able to catch the result data from listByEmail function in route and not able to send it as response. Please helpMe!!!

whites11 · Accepted Answer · 2017-08-22 10:44:03Z

In your ListByEmail function you are calling an asynchronous method, findByEmail.

When you reach the return data; line, your listByEmail function already returned so you are not returning anything to the caller.

You need to handle it asynchronously, for example:

'use strict';
var apiKey = '1xxxxxxxxL';
exports.listByEmail = function(emailid) {
    return new Promise(function(resolve, reject) {
        console.log(emailid);
        if(emailid != null && emailid != undefined) {
            var xyz = require("xyz-api")(apiKey);
            xyz.person.findByEmail(emailid, function(err, data) {
                if(data.status == 200){
                    resolve(data); // data is in json format
                }
            });
        } else {
            reject("Invalid input");
        }
    };

Then:

'use strict';
module.exports = function(app) {
    var sequel = require('../controllers/sampleController');
    app.get('/task?:email', function(req, res){
        sequel.listByEmail(req.query.email).then(function(data) {
            res.send(data);
        });
    });
};

This is a very basic example of using Promise to handle asynchronous calls in node. You should study a little bit how this works. You can start for example by reading this: https://www.promisejs.org/

Rudolf Manusachi · Accepted Answer · 2017-08-26 22:10:51Z

UPD Once you understand how to deal with callbacks, you'd better to look towards Promises, async/await, and async.js

Your function #findByEmail is asynchronous, so possibly your route should look like

'use strict';
module.exports = function(app) {
    var sequel = require('../controllers/sampleController');
    app.get('/task?:email', function(req, res){
        sequel.listByEmail(req.query.email, function(err, list){
          if(err){
            console.error(err);
            //handle error
          }
          res.send(list);
        })
    });
};

and your #listByEmail function should be like

'use strict';
var apiKey = '1xxxxxxxxL';
exports.listByEmail = function(emailid, callback) {
    console.log(emailid);
    if(emailid != null && emailid != undefined) {
        var xyz = require("xyz-api")(apiKey);
        xyz.person.findByEmail(emailid, function(err, data) {
            if(err){
              callback(err);
            } else if(data.status == 200){
                callback(null, data);
            }
        });
    }
};

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