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JavaScript

Posted by Michael Duncan
Michael Duncan
5,548 Points

Am I handling errors in my callback correctly in Node.js? (Error-first callback pattern)

TLDR: Am I handling errors in my callback function correctly?
<br> <br> I am working on a Node.js command-line application similar to the one in the exercise here. But I wanted to add more methods to the application and did not want to repeat the same request code in every one. So I've created a request helper method to handle requests using callbacks to pass the data around asynchronously (using this pattern).

If I follow this convention, however, each of my methods will all have the same bit of code to handle potential errors. Again, more repeated code that I feel like I should be avoiding.

Is this a correct way of doing this or is there a more efficient less repetitious way to handle the errors that are passed into my methods? Thanks for your help!

A method example: 

ErgastAPI.prototype.seasonsTotal = function(callback) {
  this._get(function(error, data) {
    if (error) {
      console.error(error);
      return
    }
    callback(null, data.total);
  });
}

All of my code: 

"use strict";

var http = require('http');

var ErgastAPI = function() {

}

ErgastAPI.prototype._get = function(callback) {
  http.get('http://ergast.com/api/f1/seasons2.json', function(res) {

    var body = '';
    res.on('data', function(chunk) {
      body += chunk;
    });

    res.on('end', function() {     
      if (res.statusCode === 200) {
        try {
          var parsed = JSON.parse(body);
        } catch(error) {
          return callback('Unable to parse response as JSON. (' + error.message + ')');
        }
        callback(null, parsed.MRData)    
      } else {
        callback('Error with request. (' + res.statusCode + ')');
      }
    });

  }).on('error', function(error) {
    callback('Error with the request. (' + error.message + ')');
  });

}

ErgastAPI.prototype.seasonsTotal = function(callback) {
  this._get(function(error, data) {
    if (error) {
      console.error(error);
      return
    }
    callback(null, data.total);
  });
}

var api = new ErgastAPI();

api.seasonsTotal(function(error, seasons) {
  console.log('There have been ' + seasons + ' Formula 1 seasons.');
})
Colin Marshall
Colin Marshall
32,861 Points
Colin Marshall
Colin Marshall
32,861 Points

This might be a good question for Andrew Chalkley or @Huston Hedinger. For reasons unknown, Huston is not showing up in the list of names when I try to tag him in this post.

2 Answers

Andrew Chalkley
STAFF
Andrew Chalkley
Treehouse Guest Teacher
Andrew Chalkley
Andrew Chalkley
Treehouse Guest Teacher

I prefer to use the EventEmitter pattern. Basically you emit events depending on what your code is doing and implement handlers to those events.

Take a look at my code here : https://github.com/treehouse/treehouse_blog.js and here : https://github.com/treehouse/treehouse_profile.js for inspiration.

Regards
Andrew

Michael Duncan
Michael Duncan
5,548 Points

Thanks for the response Andrew, I will take a look at this pattern and see what I can do.

Andrew Stelmach
Andrew Stelmach
12,583 Points
Andrew Stelmach
Andrew Stelmach
12,583 Points

I'm not brilliant with Javascript and Node, but it doesn't seem repetitious to me, because I can't think of a way to reduce the error handling down any more than you already have.