You Don't Know JS: Async & Performance

Foreword

Over the years, my employer has trusted me enough to conduct interviews. If we’re looking for someone with JavaScript skills, my first line of questioning…well, actually, is to check if the candidate needs the bathroom and/or a drink, because comfort is important. But once I’m past the bit about the candidate’s fluid intake/output, I set about determining if the candidate knows JavaScript, or just jQuery.

Not that there’s anything wrong with jQuery. It lets you do a lot without really knowing JavaScript, and that’s a feature—not a bug. But if the job calls for advanced skills in JavaScript performance and maintainability, you need someone who knows how libraries such as jQuery are put together. You need to be able to harness the core of JavaScript the same way they do.

If I want to get a picture of someone’s core JavaScript skill, I’m most interested in what they make of closures (you’ve read the You Don’t Know JS: Scope & Closures title of this series already, right?) and how to get the most out of asynchronicity, which brings us to this book.

For starters, you’ll be taken through callbacks, the bread and butter of asynchronous programming. Of course, bread and butter does not make for a particularly satisfying meal, but the next course is full of tasty, tasty Promises!

If you don’t know Promises, now is the time to learn. Promises are now the official way to provide async return values in both JavaScript and the DOM. All future async DOM APIs will use them, and many ...