These are my comments on Interviewing for a JavaScript Job. The story concerns a job interview, where the interviewer (“Christine”) asks the candidate (known as “The Carpenter”) to whiteboard JavaScript code solving this problem: Consider a finite checkerboard of unknown size. On each square, we ran...

“The Carpenter” was a JavaScript programmer, well-known for a meticulous attention to detail and love for hand-crafted, exquisitely joined code. The Carpenter normally worked through personal referrals, but from time to time a recruiter would slip through his screen. One such recruiter was Bob Pliss...

Nota Bene: All of the examples in this essay require ECMAScript-6, and were tested with the Babel transpiler. You can integrate Babel into your toolchain, or copy and paste the examples into its REPL in your browser. Many objects in JavaScript can model collections of things. A collection is like a ...

In our code so far (Destructuring and Recursion in ES-6 and Tail Calls, Default Arguments, and Excessive Recycling in ES-6), we have used arrays and objects to represent the structure of data, and we have extensively used the ternary operator to write algorithms that terminate when we reach a base c...

The mapWith and foldWith functions we wrote in Destructuring and Recursion in ES6 are useful for illustrating the basic principles behind using recursion to work with self-similar data structures, but they are not “production-ready” implementations. One of the reasons they are not production-ready i...

array literals Arrays are JavaScript’s “native” representation of lists. Lists are important because they represent ordered collections of things, and ordered collections are a fundamental abstraction for making sense of reality. JavaScript has a literal syntax for creating an array: The [ and ] cha...

(This was originally posted on Sunday, March 11, 2007) I recently re-read the amazing paper Why Functional Programming Matters (“WhyFP”). Although I thought that I understood WhyFP when I first read it a few years ago, when I had another look last weekend I suddenly understood that I had missed an i...

In JavaScript, you make a named function like this: function rank () { return "Captain"; } A named function is a function declaration if it appears as a statement. For example: function officer () { return rank() + " Reginald Thistleton"; function rank () { return "Captain"; } } officer() //=> 'Capt...

The tweet says it all: “I have personally found that LISP is unbelievably productive if you’re willing to invest in the 600-month learning curve.”-Paul Ford Now Mr. Ford is probably exaggerating by a factor of five: I’ll go with Peter Norvig1 and say that Lisp is unbelievably productive if you’re wi...

Paul Graham tweeted something interesting, and worth discussing. But first, a fabulous story, The Chicken and the Pig: A Pig and a Chicken are walking down the road. The Chicken says: “Hey Pig, I was thinking we should open a restaurant!” Pig replies: “Hm, maybe, what would we call it?” The Chicken ...

I was meeting Sarah for our regular coffee. Sarah’s one of those born entrepreneurs, she’s built and sold a variety of businesses, and she’s has a great touch with investments. I pick her brain about business issues, and she picks my brain about tech. As we took our seats, Sarah sighed with frustrat...

preamble As you know, you can create new objects in JavaScript using a Constructor Function, like this: function Fubar (foo, bar) { this._foo = foo; this._bar = bar; } var snafu = new Fubar("Situation Normal", "All Fsked Up"); When you “call” the constructor with the new keyword, you get a new objec...

Pattern matching is a feature found (with considerable rigor) in functional languages like Erlang and Haskell. In mathematics, algorithms and problems can often be solved by breaking them down into simple cases. Sometimes, those cases are reductions of the original problem. A famous example is the n...

Sometimes we want to share objects by reference for performance and space reasons, but we don’t want them to be mutable. One motivation is when we want many objects to be able to share a common entity without worrying that one of them may inadvertently change the common entity. JavaScript provides a...

In JavaScript, anywhere you find yourself writing: function (x) { return foo(x); } You can usually substitute just foo. For example, this code: var floats = someArray.map(function (value) { return parseFloat(value); }); Could be written: var floats = someArray.map(parseFloat); This understanding is ...

Yesterday, I read a middling article, How to Trick the Guilty and Gullible into Revealing Themselves. I wasn’t entirely fascinated by the stories about plunging arms into boiling water, or of brown M&Ms and concert venues. But then the author revealed why Nigerian 419 scammers use such blatantly rid...

One of JavaScript’s defining characteristics is its treatment of functions as first-class values. Like numbers, strings, and other kinds of objects, references to functions can be passed as arguments to functions, returned as the result from functions, bound to variables, and generally treated like ...

preface: where did the prototypes go? This essay discusses how to separate JavaScript domain properties from object behaviour, without prototypes. This is deliberate. By examining four basic ways to have one object define the behaviour of other objects, we gain insight into what we’re trying to acco...

In theory, JavaScript does not have classes. In practice, the following snippet of code is widely considered to be an example of a “class” in JavaScript: function Account () { this._currentBalance = 0; } Account.prototype.balance = function () { return this._currentBalance; } Account.prototype.depos...

I am delighted to announce that I will be joining Jeremy Ashkenas, David Nolen, Joanne Cheng, and a host of other thoughtful (and exciting!) speakers at Barcelona Future JS, May 1 – 3, 2014. Future JS is organized by the same good people who’ve organized the amazing BaRuCo (“Barcelona Ruby Conferenc...

As many people have pointed out, if you turn your head sideways and squint, the following JavaScript can be considered a “class:” function QuadTree (nw, ne, se, sw) { this._nw = nw; this._ne = ne; this._se = se; this._sw = sw; } QuadTree.prototype.population = function () { return this._nw.populatio...

Hal comes home after work, flips the light switch. Hmm, bulb’s burned out. Into the cupboard to grab a replacement. While grabbing the box of bulbs, he notices that the shelf is loose. It seems one of the supports has a loose wood screw. Off to the kitchen, where he pulls open a drawer to get the sc...

The word “inheritance” is widely used when talking about object-oriented programming. People will say things like “Objects inherit methods from classes,” or perhaps “Subclasses inherit behaviour from superclasses,” and sometimes they won’t even say what is being inherited: “Cow inherits from Ungulat...

Ruby allows you to make private methods: class Sample def foo :SNAFU end private def private_foo :PRIVATE_SNAFU end end Sample.new.foo #=> :SNAFU Sample.new.private_foo #=> NoMethodError: private method `private_foo' called for #<Sample:0x007fa12192e130> Ruby also allows you to make what other langu...

Many people can and do say that “JavaScript has classes.” As a very rough, hand-wavy way of saying that “JavaScript has things that define the characteristics of one or more objects,” this is true. And many people lead healthy, happy, and productive lives without caring whether this statement is act...

The new keyword in JavaScript is very straightforward to use: function Rectangle (x, y) { this.x = x; this.y = y; } var rect = new Rectangle(2, 3); rect.x //=> 2 When a function is called with the new keyword, a new object is created and that object becomes the context of the function call. That con...

Everybody was type-fu fighting Compiling fast as lightning In fact it was a little bit frightening But their code had early binding They were funky ML men from funky CAML town They were chopping classes up and they were chopping classes down It’s the ancient Curry’s art, in Haskell but not Dart It’s...

The other day, a colleague and I were debating whether to defactor some code. No, not refactor the code, de-factor the code. what is “factoring?” Defactoring is the process of removing factoring from code. The word “refactoring” is commonplace, “factoring” is somewhat less common, and “defactoring” ...

In Ruby, modules are often used to mix functionality into concrete classes. Another excellent pattern is to extend objects as a way of avoiding monkey-patching classes you do not “own.” There’s a third pattern that I find handy and expressive: Using modules as object predicates. Let’s begin by defin...

As programmers, it is our job to build software out of abstractions. Logic gates are connected to form a “Von Neumann Computer.” An assembler creates an interface that can be programmed with instructions like MOV 12345, 567890. A compiler lets us write x = y, and so on up to has_and_belongs_to_many ...