Over a million developers have joined DZone.

JavaScript: How to Define and Process a Promise Object

DZone's Guide to

JavaScript: How to Define and Process a Promise Object

In this post, I'll provide direction and code samples on how to create and use a Promise Object in JavaScript. Read on to see how it's done.

· Web Dev Zone
Free Resource

Never build auth again! Okta makes it simple to implement authentication, authorization, MFA and more in minutes. Try the free developer API today! 

This article provides tips and code samples on how to define and process a Promise object. Please feel free to comment/suggest if I failed to mention one or more important points. 

How to Define a Promise Object

The following example demonstrates an Auth module within an API login that returns a Promise that will either be resolved/fulfilled or rejected.  The returned object, will represent a domain object such as User or Error object with a status and error message, as demonstrated below:

// Promise needs to be imported when executing a module using Node
var Promise = require("promise");

function Auth() {

Auth.prototype.login = function(user) {
    return new Promise(function(resolve, reject) {
        if(user.username != "" && user.password != "") {
            resolve({username: user.username, age: 21, location: "Hyderabad", firstname: "Raju", lastname: "Mastana"});
        } else {
            if(user.username == ""){
                reject({status:1, message: "Username is invalid"});
            } else {
                reject({status:2, message: "Password is invalid"});

module.exports = Auth;

How to Process a Promise Object

The following tasks are defined in the code sample provided, which calls login API on an Auth object:

  • Create an Auth object
  • Invoke login API on Auth object
  • Invoke "then" method on Promise object returned from the invocation of login API.
// Import the Auth module
var Auth = require('./Auth');

// Create an Auth object
var auth = new Auth();
// Calls login API on Auth object
// Returns a promise object
var loginPromise = auth.login({username:'', password:'pass123'});
// Once the state of Promise is fulfilled/resolved or rejected,
// following is executed
    console.log("User name: " + response.name);
}, function(error) {

Launch your application faster with Okta’s user management API. Register today for the free forever developer edition!

javascript ,angular js ,promise ,promises ,promises in javascript

Published at DZone with permission of Ajitesh Kumar, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.


Dev Resources & Solutions Straight to Your Inbox

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.


{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}