Since promises were added to JavaScript in 2015, they have become an integral part of the language. A good understanding of how promises work is more important than ever in becoming a proficient JavaScript developer. This book begins by explaining the basic concepts behind promises, including what they are, how to use them, and how to create your own. You'll then build upon these basic concepts to learn how to chain promises together and how to respond to multiple promises at once. Once you've learned these advanced concepts, you'll move on to learn how promises work with async functions and how to track unhandled promise rejections. All of the concepts discussed are grounded in real world examples so you learn not just how to use a particular technique, but also why and when to use it. It doesn't matter if you're writing JavaScript for web browsers, Node.js, or Deno, this book will teach you everything you need to know about promises.

ECMAScript 6 represents the biggest update to the core of JavaScript in the history of the language. In Understanding ECMAScript 6, expert developer Nicholas C. Zakas provides a complete guide to the object types, syntax, and other exciting changes that ECMAScript 6 brings to JavaScript. Every chapter is packed with example code that works in any JavaScript environment so you'll be able to see new features in action.

You'll learn:
-How ECMAScript 6 class syntax relates to more familiar JavaScript concepts
-What makes iterators and generators useful
-How arrow functions differ from regular functions
-Ways to store data with sets, maps, and more
-The power of inheritance
-How to improve asynchronous programming with promises
-How modules change the way you organize code

Whether you're a web developer or a Node.js developer, you'll find Understanding ECMAScript 6 indispensable on your journey from ECMAScript 5 to ECMAScript 6.

If you're like most developers, you rely heavily on JavaScript to build interactive and quick-responding web applications. The problem is that all of those lines of JavaScript code can slow down your apps. This book reveals techniques and strategies to help you eliminate performance bottlenecks during development. You'll learn how to improve execution time, downloading, interaction with the DOM, page life cycle, and more.

Yahoo frontend engineer Nicholas C. Zakas and five other JavaScript experts--Ross Harmes, Julien Lecomte, Steven Levithan, Stoyan Stefanov, and Matt Sweeney--demonstrate optimal ways to load code onto a page, and offer programming tips to help your JavaScript run as efficiently and quickly as possible. You'll learn the best practices to build and deploy your files to a production environment, and tools that can help you find problems once your site goes live.

• Identify problem code and use faster alternatives to accomplish the same task
• Improve scripts by learning how JavaScript stores and accesses data
• Implement JavaScript code so that it doesn't slow down interaction with the DOM
• Use optimization techniques to improve runtime performance
• Learn ways to ensure the UI is responsive at all times
• Achieve faster client-server communication
• Use a build system to minify files, and HTTP compression to deliver them to the browser

You may have definite ideas about writing code when working alone, but team development requires that everyone use the same approach. With the JavaScript practices in this book--including code style, programming tips, and automation--you will learn how to write maintainable code that other team members can easily understand, adapt, and extend.

Author Nicholas Zakas assembled this collection of best practices as a front-end tech leader at Yahoo!, after completing his own journey from solo hacker to team player. He also includes rules recommended by other industry authorities. Use these tips and techniques to help your team set aside individual preferences and function at a higher level.

• Establish specific code conventions for your team
• Use tools such as JSLint and JSHint to keep your team on track
• Adopt style guidelines, such as basic formatting, to help your team produce uniform code
• Apply several programming practices to solve problems and improve code quality
• Create an automated JavaScript build system using a variety of utilities
• Integrate browser-based JavaScript testing with tools such as the YUI Test Selenium Driver