Search icon CANCEL
Subscription
0
Cart icon
Your Cart (0 item)
Close icon
You have no products in your basket yet
Arrow left icon
Explore Products
Best Sellers
New Releases
Books
Videos
Audiobooks
Learning Hub
Free Learning
Arrow right icon
Advanced JavaScript
Advanced JavaScript

Advanced JavaScript: Speed up web development with the powerful features and benefits of JavaScript

eBook
$17.99 $26.99
Paperback
$38.99
Subscription
Free Trial
Renews at $19.99p/m

What do you get with Print?

Product feature icon Instant access to your digital eBook copy whilst your Print order is Shipped
Product feature icon Paperback book shipped to your preferred address
Product feature icon Download this book in EPUB and PDF formats
Product feature icon Access this title in our online reader with advanced features
Product feature icon DRM FREE - Read whenever, wherever and however you want
Product feature icon AI Assistant (beta) to help accelerate your learning
OR
Modal Close icon
Payment Processing...
tick Completed

Shipping Address

Billing Address

Shipping Methods
Table of content icon View table of contents Preview book icon Preview Book

Advanced JavaScript

Chapter 2. Asynchronous JavaScript

Learning Objectives

By the end of this chapter, you will be able to:

  • Define asynchronous programming

  • Characterize the JavaScript event loop

  • Utilize callbacks and promises to write asynchronous code

  • Simplify asynchronous code with async/await syntax

In this chapter, we shall learn Asynchronous JavaScript and its uses.

Introduction


In the previous chapter, we covered many of the new and powerful features released in ES6. We discussed the evolution of JavaScript and highlighted the key additions in ES6. We discussed scope rules, variable declaration, arrow functions, template literals, enhanced object properties, destructuring assignment, classes and modules, transpiling, and iterators and generators.

In this chapter, we will learn what an asynchronous programming language is and how to write and understand asynchronous code. In the first topic, we will define asynchronous programming and show how JavaScript is an asynchronous, event driven programming language. Then, we will outline callbacks and show how to use callbacks to write asynchronous JavaScript. We will then define promises and demonstrate how to use promises to write asynchronous JavaScript. In the final topic, we will present the async/await syntax and simplify our asynchronous code using promises and this syntax.

Asynchronous Programming


JavaScript is a single threaded, event driven, asynchronous programming language. What does this mean? This means that JavaScript runs on a single thread and delays/handles certain events or function calls through an event queue. We will break down the basics of how JavaScript does this through the following topic.

Sync Versus Async

What does it mean for code to be synchronous or asynchronous? These two buzzwords get thrown around a lot in JavaScript. Synchronous is derived from the Greek root syn, meaning "with", and chronos, which means "time". Synchronous literally means "with time", or rather, code that is coordinated with time. Lines of code are run one at a time and are not started until the previous line has been handled. Asynchronous, or async, is derived from the Greek root async, meaning "not with", and chronos, hence asynchronous literally means "not with time" or rather, code that is not coordinated with time. The order code that is run is not coordinated...

Callbacks


Callbacks are the most basic form of JavaScript asynchronous programming. In the simplest terms, a callback is a function that gets called after another function completes. Callbacks are used to handle the response of an asynchronous function call.

In JavaScript, functions are treated like objects. They can be passed around as arguments, returned by functions, and saved into variables. A callback is a function object that is passed as an argument into a higher order function. A higher order function is simply a mathematics and computer science term for a function that takes one or more functions as arguments (callbacks) or returns a function. In JavaScript, a higher order function will take a callback as a parameter. Once the higher order finishes doing some form of work, such as an HTTP request or database call, it calls the callback function with the error or return values.

As mentioned in the Event Loop section in Asynchronous Programming, JavaScript is an event driven language...

Promises


In JavaScript, a promise is an object that wraps an asynchronous operation and notifies the program when the asynchronous operation completes. The promise object represents the eventual completion or failure of the wrapped operation. A promise is a proxy for a value not necessarily known. Instead of providing the value immediately, like a synchronous program, it promises to provide a value at some point in the future. Promises allow you to associate success and error handlers with an asynchronous action. These handlers are called at the completion or failure of the wrapped asynchronous process.

Promises States

Every promise has a state. A promise can only succeed with a value or fail with an error once. The state of a promise defines where the promise is in its work towards the resolution of a value.

A promise comes in three states: pending, fulfilled, or rejected. A promise starts in the pending state. This means that the async operation being done inside the promise is not complete...

Async/Await


Async/await is a new syntax form added to simplify code that uses promises. Async/await introduces two new keywords: async and await. Async is added to function declarations and await is used inside an async function. It is surprisingly easy to understand and use. In its simplest form, async/await allows us to write promise-based asynchronous code that looks almost identical to the synchronous code that does the same task. We will use async/await to simplify code using promises and make it even easier to read and understand.

Async/Await Syntax

The async keyword is added to function declarations; it must precede the function keyword. An async function declaration defines an asynchronous function. An example declaration of an async function is shown in the following snippet:

async function asyncExample( /* arguments */  ){ /* do work */ }

Snippet 2.34: Implementing promises

An async function implicitly returns a promise, no matter what the return value is specified to be. If the return...

Summary


JavaScript is an asynchronous, event-driven, single-threaded language. Instead of hanging during a long-running operation to another resource, JavaScript does work on other operations if any work is pending. JavaScript accomplishes this with the event loop. The event loop is composed of the call stack, heap, event queue, and main event loop. These four components work together to schedule when JavaScript runs different parts of the code. To leverage JavaScript's asynchronous nature, we use callbacks or promises. Callbacks are simply functions passed as arguments into other functions. Promises are special classes with event handler functions. When an asynchronous operation finishes, the JavaScript engine runs the callback or calls the promise handler attached to that operation's complete event. This is asynchronous JavaScript in its simplest form.

In the next chapter, we will learn about the Document Object Model (DOM), the JavaScript event object, and the jQuery library.

Left arrow icon Right arrow icon

Key benefits

  • Explore the new ES6 syntax, the event loop, and asynchronous programming
  • Learn the test-driven development approach when building apps
  • Master advanced JavaScript concepts to enhance your web developments skill

Description

If you are looking for a programming language to develop flexible and efficient applications, JavaScript is an obvious choice. Advanced JavaScript is a hands-on guide that takes you through JavaScript and its many features, one step at a time. You'll begin by learning how to use the new JavaScript syntax in ES6, and then work through the many other features that modern JavaScript has to offer. As you progress through the chapters, you’ll use asynchronous programming with callbacks and promises, handle browser events, and perform Document Object Model (DOM) manipulation. You'll also explore various methods of testing JavaScript projects. In the concluding chapters, you'll discover functional programming and learn to use it to build your apps. With this book as your guide, you'll also be able to develop APIs using Node.js and Express, create front-ends using React/Redux, and build mobile apps using React/Expo. By the end of Advanced JavaScript, you will have explored the features and benefits of JavaScript to build small applications.

Who is this book for?

This book is designed to target anyone who wants to write JavaScript in a professional environment. We expect the audience to have used JavaScript in some capacity and be familiar with the basic syntax. This book would be good for a tech enthusiast wondering when to use generators or how to use Promises and Callbacks effectively, or a novice developer who wants to deepen their knowledge on JavaScript and understand TDD.

What you will learn

  • Examine major features in ES6 and implement those features to build applications
  • Create promise and callback handlers to work with asynchronous processes
  • Develop asynchronous flows using Promise chaining and async/await syntax
  • Manipulate the DOM with JavaScript
  • Handle JavaScript browser events
  • Explore Test Driven Development and build code tests with JavaScript code testing frameworks.
  • List the benefits and drawbacks of functional programming compared to other styles
  • Construct applications with the Node.js backend framework and the React frontend framework
Estimated delivery fee Deliver to South Africa

Standard delivery 10 - 13 business days

$12.95

Premium delivery 3 - 6 business days

$34.95
(Includes tracking information)

Product Details

Country selected
Publication date, Length, Edition, Language, ISBN-13
Publication date : Jan 31, 2019
Length: 330 pages
Edition : 1st
Language : English
ISBN-13 : 9781789800104
Languages :
Tools :

What do you get with Print?

Product feature icon Instant access to your digital eBook copy whilst your Print order is Shipped
Product feature icon Paperback book shipped to your preferred address
Product feature icon Download this book in EPUB and PDF formats
Product feature icon Access this title in our online reader with advanced features
Product feature icon DRM FREE - Read whenever, wherever and however you want
Product feature icon AI Assistant (beta) to help accelerate your learning
OR
Modal Close icon
Payment Processing...
tick Completed

Shipping Address

Billing Address

Shipping Methods
Estimated delivery fee Deliver to South Africa

Standard delivery 10 - 13 business days

$12.95

Premium delivery 3 - 6 business days

$34.95
(Includes tracking information)

Product Details

Publication date : Jan 31, 2019
Length: 330 pages
Edition : 1st
Language : English
ISBN-13 : 9781789800104
Languages :
Tools :

Packt Subscriptions

See our plans and pricing
Modal Close icon
$19.99 billed monthly
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Simple pricing, no contract
$199.99 billed annually
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Choose a DRM-free eBook or Video every month to keep
Feature tick icon PLUS own as many other DRM-free eBooks or Videos as you like for just $5 each
Feature tick icon Exclusive print discounts
$279.99 billed in 18 months
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Choose a DRM-free eBook or Video every month to keep
Feature tick icon PLUS own as many other DRM-free eBooks or Videos as you like for just $5 each
Feature tick icon Exclusive print discounts

Frequently bought together


Stars icon
Total $ 131.97
Advanced JavaScript
$38.99
Professional JavaScript
$43.99
Modern JavaScript Web Development Cookbook
$48.99
Total $ 131.97 Stars icon
Banner background image

Table of Contents

6 Chapters
Introducing ECMAScript 6 Chevron down icon Chevron up icon
Asynchronous JavaScript Chevron down icon Chevron up icon
DOM Manipulation and Event Handling Chevron down icon Chevron up icon
Testing JavaScript Chevron down icon Chevron up icon
Functional Programming Chevron down icon Chevron up icon
The JavaScript Ecosystem Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Half star icon Empty star icon 3.5
(4 Ratings)
5 star 25%
4 star 0%
3 star 75%
2 star 0%
1 star 0%
FM Jul 02, 2022
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Forget about what people are saying below about the book and the dumb reviews. This book is by far the best JS book I've ordered so far! It's modern JS, covers all the points you need and more. If you want a book about design patterns, look elsewhere. But design paterns are general and applicable to (almost) every programming language out there. The book does what says on the cover, shows you concepts both basic and advanced! 5 stars from me!
Amazon Verified review Amazon
Lee Apr 27, 2024
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
I've only almost completed the first chapter, the concepts introduced herein are clear and precise, but the amount of errata is very distracting. Most errata encountered thus far were likely caused by copying and pasting codes that are repeated throughout the same section of narrative. I wish all Packt represented books could receive stricter typo and errata screening, because this class of flaws has been around for way too long. Both authors and publishers have their responsibilities to make their books relatively joyful to read. I also think that customers should be provided with reading tools that allow the highlighting of typo and errata and the input of their reasons and correction suggestions. I requested these in multiple conversations with their reps already.
Subscriber review Packt
Mark cooper Feb 24, 2021
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
Decent overview of several core Javascript areas. A little disjointed (went from a chapter on asynchronous programming to one on the DOM and jQuery) but overall worth the money.
Amazon Verified review Amazon
Scott J Pearson Aug 15, 2021
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
In the past decade, the JavaScript language has witnessed a renaissance of new activity. Once pigeon-holed as a language for web browser eye-candy, JavaScript can now be used for the entire stack (server-side, client-side, testing, and even command-line). In this book, Shute attempts to keep developers up to date with a high-level review of the advancements. While this book is not a classic (and what modern computer-language-specific book is a classic?), it serves the needs of the IT community quite well.Shute starts by informing readers about the modernization of JavaScript in a form cryptically called ES6. This language allows for more compact and more powerful expression, including new features dealing with asynchronous functions. Most programmers who have done a deep dive into some form of JavaScript are familiar with the challenges of its asynchronous nature.In case anyone is still not familiar with the Document Object Model (DOM) and jQuery, a tutorial is provided. (Most programmers will likely not gain much other than review from this section.) A section on automated testing is provided along with a conceptual introduction to functional programming. Finally, the “ecosystem” of Node.js, Express, and React are described in broader terms.As you can see, Shute does not miss much of the recent developments. However, he stays pretty high in his overview and provides few deep dives to entertain readers as well. This is the main limitation of the book. For instance, I bought another book on Node.js to supplement while reading this one. That said, this book did inspire me to buy a book instead of merely being bored in the first place – a definite accomplishment.This book’s intended audience really consists of only the software development community – hence its higher price-tag. The materials were put together well with a sturdy cover and clear font. Due to the technical content, few pictures accompany the text. Overall, this book updated me on a high level but left me wanting to take a deep dive or two into more difficult (and interesting) topics.
Amazon Verified review Amazon
Get free access to Packt library with over 7500+ books and video courses for 7 days!
Start Free Trial

FAQs

What is the delivery time and cost of print book? Chevron down icon Chevron up icon

Shipping Details

USA:

'

Economy: Delivery to most addresses in the US within 10-15 business days

Premium: Trackable Delivery to most addresses in the US within 3-8 business days

UK:

Economy: Delivery to most addresses in the U.K. within 7-9 business days.
Shipments are not trackable

Premium: Trackable delivery to most addresses in the U.K. within 3-4 business days!
Add one extra business day for deliveries to Northern Ireland and Scottish Highlands and islands

EU:

Premium: Trackable delivery to most EU destinations within 4-9 business days.

Australia:

Economy: Can deliver to P. O. Boxes and private residences.
Trackable service with delivery to addresses in Australia only.
Delivery time ranges from 7-9 business days for VIC and 8-10 business days for Interstate metro
Delivery time is up to 15 business days for remote areas of WA, NT & QLD.

Premium: Delivery to addresses in Australia only
Trackable delivery to most P. O. Boxes and private residences in Australia within 4-5 days based on the distance to a destination following dispatch.

India:

Premium: Delivery to most Indian addresses within 5-6 business days

Rest of the World:

Premium: Countries in the American continent: Trackable delivery to most countries within 4-7 business days

Asia:

Premium: Delivery to most Asian addresses within 5-9 business days

Disclaimer:
All orders received before 5 PM U.K time would start printing from the next business day. So the estimated delivery times start from the next day as well. Orders received after 5 PM U.K time (in our internal systems) on a business day or anytime on the weekend will begin printing the second to next business day. For example, an order placed at 11 AM today will begin printing tomorrow, whereas an order placed at 9 PM tonight will begin printing the day after tomorrow.


Unfortunately, due to several restrictions, we are unable to ship to the following countries:

  1. Afghanistan
  2. American Samoa
  3. Belarus
  4. Brunei Darussalam
  5. Central African Republic
  6. The Democratic Republic of Congo
  7. Eritrea
  8. Guinea-bissau
  9. Iran
  10. Lebanon
  11. Libiya Arab Jamahriya
  12. Somalia
  13. Sudan
  14. Russian Federation
  15. Syrian Arab Republic
  16. Ukraine
  17. Venezuela
What is custom duty/charge? Chevron down icon Chevron up icon

Customs duty are charges levied on goods when they cross international borders. It is a tax that is imposed on imported goods. These duties are charged by special authorities and bodies created by local governments and are meant to protect local industries, economies, and businesses.

Do I have to pay customs charges for the print book order? Chevron down icon Chevron up icon

The orders shipped to the countries that are listed under EU27 will not bear custom charges. They are paid by Packt as part of the order.

List of EU27 countries: www.gov.uk/eu-eea:

A custom duty or localized taxes may be applicable on the shipment and would be charged by the recipient country outside of the EU27 which should be paid by the customer and these duties are not included in the shipping charges been charged on the order.

How do I know my custom duty charges? Chevron down icon Chevron up icon

The amount of duty payable varies greatly depending on the imported goods, the country of origin and several other factors like the total invoice amount or dimensions like weight, and other such criteria applicable in your country.

For example:

  • If you live in Mexico, and the declared value of your ordered items is over $ 50, for you to receive a package, you will have to pay additional import tax of 19% which will be $ 9.50 to the courier service.
  • Whereas if you live in Turkey, and the declared value of your ordered items is over € 22, for you to receive a package, you will have to pay additional import tax of 18% which will be € 3.96 to the courier service.
How can I cancel my order? Chevron down icon Chevron up icon

Cancellation Policy for Published Printed Books:

You can cancel any order within 1 hour of placing the order. Simply contact [email protected] with your order details or payment transaction id. If your order has already started the shipment process, we will do our best to stop it. However, if it is already on the way to you then when you receive it, you can contact us at [email protected] using the returns and refund process.

Please understand that Packt Publishing cannot provide refunds or cancel any order except for the cases described in our Return Policy (i.e. Packt Publishing agrees to replace your printed book because it arrives damaged or material defect in book), Packt Publishing will not accept returns.

What is your returns and refunds policy? Chevron down icon Chevron up icon

Return Policy:

We want you to be happy with your purchase from Packtpub.com. We will not hassle you with returning print books to us. If the print book you receive from us is incorrect, damaged, doesn't work or is unacceptably late, please contact Customer Relations Team on [email protected] with the order number and issue details as explained below:

  1. If you ordered (eBook, Video or Print Book) incorrectly or accidentally, please contact Customer Relations Team on [email protected] within one hour of placing the order and we will replace/refund you the item cost.
  2. Sadly, if your eBook or Video file is faulty or a fault occurs during the eBook or Video being made available to you, i.e. during download then you should contact Customer Relations Team within 14 days of purchase on [email protected] who will be able to resolve this issue for you.
  3. You will have a choice of replacement or refund of the problem items.(damaged, defective or incorrect)
  4. Once Customer Care Team confirms that you will be refunded, you should receive the refund within 10 to 12 working days.
  5. If you are only requesting a refund of one book from a multiple order, then we will refund you the appropriate single item.
  6. Where the items were shipped under a free shipping offer, there will be no shipping costs to refund.

On the off chance your printed book arrives damaged, with book material defect, contact our Customer Relation Team on [email protected] within 14 days of receipt of the book with appropriate evidence of damage and we will work with you to secure a replacement copy, if necessary. Please note that each printed book you order from us is individually made by Packt's professional book-printing partner which is on a print-on-demand basis.

What tax is charged? Chevron down icon Chevron up icon

Currently, no tax is charged on the purchase of any print book (subject to change based on the laws and regulations). A localized VAT fee is charged only to our European and UK customers on eBooks, Video and subscriptions that they buy. GST is charged to Indian customers for eBooks and video purchases.

What payment methods can I use? Chevron down icon Chevron up icon

You can pay with the following card types:

  1. Visa Debit
  2. Visa Credit
  3. MasterCard
  4. PayPal
What is the delivery time and cost of print books? Chevron down icon Chevron up icon

Shipping Details

USA:

'

Economy: Delivery to most addresses in the US within 10-15 business days

Premium: Trackable Delivery to most addresses in the US within 3-8 business days

UK:

Economy: Delivery to most addresses in the U.K. within 7-9 business days.
Shipments are not trackable

Premium: Trackable delivery to most addresses in the U.K. within 3-4 business days!
Add one extra business day for deliveries to Northern Ireland and Scottish Highlands and islands

EU:

Premium: Trackable delivery to most EU destinations within 4-9 business days.

Australia:

Economy: Can deliver to P. O. Boxes and private residences.
Trackable service with delivery to addresses in Australia only.
Delivery time ranges from 7-9 business days for VIC and 8-10 business days for Interstate metro
Delivery time is up to 15 business days for remote areas of WA, NT & QLD.

Premium: Delivery to addresses in Australia only
Trackable delivery to most P. O. Boxes and private residences in Australia within 4-5 days based on the distance to a destination following dispatch.

India:

Premium: Delivery to most Indian addresses within 5-6 business days

Rest of the World:

Premium: Countries in the American continent: Trackable delivery to most countries within 4-7 business days

Asia:

Premium: Delivery to most Asian addresses within 5-9 business days

Disclaimer:
All orders received before 5 PM U.K time would start printing from the next business day. So the estimated delivery times start from the next day as well. Orders received after 5 PM U.K time (in our internal systems) on a business day or anytime on the weekend will begin printing the second to next business day. For example, an order placed at 11 AM today will begin printing tomorrow, whereas an order placed at 9 PM tonight will begin printing the day after tomorrow.


Unfortunately, due to several restrictions, we are unable to ship to the following countries:

  1. Afghanistan
  2. American Samoa
  3. Belarus
  4. Brunei Darussalam
  5. Central African Republic
  6. The Democratic Republic of Congo
  7. Eritrea
  8. Guinea-bissau
  9. Iran
  10. Lebanon
  11. Libiya Arab Jamahriya
  12. Somalia
  13. Sudan
  14. Russian Federation
  15. Syrian Arab Republic
  16. Ukraine
  17. Venezuela