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It’s official! We’re getting a new function syntax! The TC39 group (the panel charged with delivering ES 6) has reached consensus on an abbreviated syntax for JavaScript function expressions. Its popularly known as the fat arrow syntax, and is based on a similar construct found in CoffeeScript. Make no mistake, I’m delighted that we will finally have an alternative to the unnecessary clunkiness an

Most built-in JavaScript types are constructors whose prototypes contain the methods and other properties that define their default behavior: //(results will vary by browser) Object.getOwnPropertyNames(Function.prototype) //["bind", "arguments", "toString", "length", "call", "name", "apply", "caller", "constructor"] You can’t delete or replace a native prototype, but you can edit the values of its

You may not know it but, in JavaScript, whenever you interact with string, number or boolean primitives you enter a hidden world of object shadows and coercion. So dust off your Sherlock Holmes outfit and read on… The basics Objects are aggregations of properties. A property can reference an object or a primitive. Primitives are values, they have no properties. In JavaScript there are 5 primitive

What’s wrong with typeof? The most glaring issue is that typeof null returns “object”. It’s simply a mistake. There’s talk of fixing it in the next version of the ECMAScript specification, although this would undoubtedly introduce backwards compatibility issues. var a; typeof a; //"undefined" typeof b; //"undefined" alert(a); //undefined alert(b); //ReferenceError Other than that, typeof is just n

(In Portugese) The JavaScript this keyword is ubiquitous yet misconceptions abound. What you need to know Every execution context has an associated ThisBinding whose lifespan is equal to that of the execution context and whose value is constant. There are three types of execution context: global, function and evaluation. Here’s a tabular summary followed by a little more detail, and some examples:

You don’t have to be a JavaScript novice to get confused by this… if ([0]) { console.log([0] == true); //false console.log(!![0]); //true } or this… if ("potato") { console.log("potato" == false); //false console.log("potato" == true); //false } The good news is that there is a standard and all browsers follow it. Some authors will tell you to fear coercion and and code against it. I hope to persu

Global variables should be reserved for objects that have system-wide relevance and they should be named to avoid ambiguity and minimize the risk of naming collisions. In practice this means you should avoid creating global objects unless they are absolutely necessary. But, hey, you already knew all that….. So what do you do about it? Conventional wisdom tells us that the best global abatement str

Most browsers are coalescing around a consistent API for defining JavaScript Getters and Setters. I’m not entirely comfortable with custom getters and setters – JavaScript’s clean syntax is now a little murkier, and we have a new pitfall to avoid when iterating and cloning object properties, not to mention a significant risk of involuntary recursion – but still I’ll admit they have their uses. I’m

In JavaScript, a closure is a function to which the variables of the surrounding context are bound by reference. function getMeAClosure() { var canYouSeeMe = "here I am"; return (function theClosure() { return {canYouSeeIt: canYouSeeMe ? "yes!": "no"}; }); } var closure = getMeAClosure(); closure().canYouSeeIt; //"yes!" Every JavaScript function forms a closure on creation. In a moment I’ll explai

(versión abreviada en español) If you think the introduction of Array.prototype.forEach and friends will send the for-loop the way of the dodo, think again. There’s life in the old dog yet. The for-loop is often seen as something of a one trick pony, most suited to the classic form of list iteration: for (var i=0; i<arr.length; i++) { //do something to each member } but with the wealth of higher o

(en Español, русском, 中文) JavaScript’s prototype object generates confusion wherever it goes. Seasoned JavaScript professionals, even authors frequently exhibit a limited understanding of the concept. I believe a lot of the trouble stems from our earliest encounters with prototypes, which almost always relate to new, constructor and the very misleading prototype property attached to functions. In

Behold, the new hotness! The shapely Arrow Function has driven away the irksome function keyword and (by virtue of lexical this scoping) bought joy to many a JavaScript programmer. Yet, as the following account relates, even the best tools should be used with discretion. Continue reading “Of Classes and Arrow Functions (a cautionary tale)” → I wrote a book called If Hemingway Wrote JavaScript in w

The native JavaScript function indexOf, applied to a String, returns the index of the first occurrence of a specified value. Useful as it is, I often find myself wishing for a variant method that will return the index after the occurrence so that I can pass the result to a slice call and return everything after a given character. With this in mind, I created a method called express (as in expressi