Kyle Simpson - You Dont Know JS

by Kyle Simpson

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[LSI]

Over the years, my employer has trusted me enough to conduct interviews.If were looking for someone with JavaScript skills, my first line ofquestioningwell, actually, is to check if the candidateneeds the bathroom and/or a drink, because comfort is important. Butonce Im past the bit about the candidates fluid intake/output, I setabout determining if the candidate knows JavaScript, or just jQuery.

Not that theres anything wrong with jQuery. It lets you do a lotwithout really knowing JavaScript, and thats a featurenot a bug. Butif the job calls for advanced skills in JavaScript performance andmaintainability, you need someone who knows how libraries such as jQueryare put together. You need to be able to harness the core of JavaScriptthe same way they do.

If I want to get a picture of someones core JavaScript skill, Im mostinterested in what they make of closures (youve read the You Dont Know JS: Scope & Closures title of thisseries already, right?) and how to get the most out of asynchronicity,which brings us to this book.

For starters, youll be taken through callbacks, the bread and butter ofasynchronous programming. Of course, bread and butter does not make fora particularly satisfying meal, but the next course is full of tasty,tasty Promises!

If you dont know Promises, now is the time to learn. Promises are nowthe official way to provide async return values in both JavaScript andthe DOM. All future async DOM APIs will use them, and many already do, so beprepared! At the time of writing, Promises have shipped in most majorbrowsers, with IE shipping soon. Once youve finished savoring Promises, I hope youleft room for the next course, Generators.

Generators snuck their way into stable versions of Chrome and Firefoxwithout too much pomp and ceremony, because, frankly, theyre morecomplicated than they are interesting. Or, thats what I thoughtuntil I saw them combined with Promises. There, they become an importanttool in readability and maintenance.

For dessert, well, I wont spoil the surprise, but prepare to gaze intothe future of JavaScript! This book covers features that give you more and more controlover concurrency and asynchronicity.

Well, I wont block your enjoyment of the book any longeron with theshow! If youve already read part of the book before reading thisforeword, give yourself 10 asynchronous points! You deserve them!

Jake Archibald (http://jakearchibald.com, @jaffathecake), Developer Advocate at Google Chrome