In this essay, we are going to look at recursive algorithms, and how sometimes, we can organize an algorithm so that it resembles the data structure it manipulates, and organize a data structure so that it resembles the algorithms that manipulate it. When algorithms and the data structures they mani...

In this essay, we will take a look at some higher-order functions, with an eye to seeing how they can be used to make our programs more expressive, while balancing that against the need to limit the perceived complexity of our programs. introduction: expressiveness One of the most basic ideas in pro...

Unfolded, © 2011 Regulla, Some rights reserved preamble: unfolds and folds Anamorphisms are functions that map from some object to a more complex structure containing the type of the object. For example, mapping from an integer to a list of integers. Here’s an anamorphism: function downToOne(n) { co...

In Why Are Mixins Considered Harmful, we saw that concatenative sharing–as exemplified by mixins–leads to snowballing complexity because of three effects: Lack of Encapsulation Implicit Dependencies Name Clashes We looked at some variations on creating encapsulation to help reduce the “surface area”...

update: Part II, From Mixins to Object Composition is now available. In Mixins Considered Harmful, Dan Abramov wrote something that sounds familiar to everyone1 who works with legacy applications: Some of our code using React gradually became incomprehensible. Occasionally, the React team would see ...

the hubris of blog post authors Althea and Ben were sipping feature espressos at their local indie coffee shop. “Althea,” Ben began, “I’m prepping for interviews with you-know-who, so I’ve been trying to read as many algorithm blog posts as I can, just to catch up on all the stuff I’ve forgotten now...

larry wall laziness and eagerness In computing, “laziness” is a broad term, generally referring to not doing any work unless you need it. Whereas its opposite is “eagerness,” doing as much work as possible in case you need it later. Consider this JavaScript: function ifThen (a, b) { if (a) return b;...

hal abelson the fibonacci numbers In mathematics, the Fibonacci numbers or Fibonacci sequence are numbers in the following integer sequence: 0, 1, 1, 2, 3, 5, 8, 13, 21, ….1 The rule for determining the sequence is quite simple to explain: The first number is 0. The second number is 1. Every subsequ...

foreword This talk was given at NDC London on January 14, 2016. This is not a literal transcript: A selection of the original slides are shown here, along with some annotations explaining the ideas presented. Part I: The Basics “In object-oriented programming, the command pattern is a behavioural de...

A trait is a concept used in object-oriented programming: a trait represents a collection of methods that can be used to extend the functionality of a class. Essentially a trait is similar to a class made only of concrete methods that is used to extend another class with a mechanism similar to multi...

Mixins solve a very common problem in class-centric OOP: For non-trivial applications, there is a messy many-to-many relationship between behaviour and classes, and it does not neatly decompose into a tree. In this essay, we only touch lightly over the benefits of using mixins with classes, and in t...

I highly recommend reading Justin Fagnani’s “Real” Mixins with JavaScript Classes. To summarize my understanding, Justin likes using “mixins,” but takes issue with the way they are implemented as described in things like Using ES7 Decorators as Mixins.1 Justin wants to be able to have a fully open m...

Once upon a time, programming interviews would include a fizz-buzz problem to weed out the folks who couldn’t string together a few lines of code. We can debate when and how such things are appropriate interview questions, but one thing that is always appropriate is to use them as inspiration for pr...

a fizz-buzz problem Job interviews sometimes contain simple programming tasks. Often called “fizz-buzz problems,” the usual purpose is to quickly weed out hopefuls who can’t actually program anything. Here’s an example, something that might be used in a phone screen or an in-person interview with pr...

Once upon a time, there was a language called C,1 and this language had something called a struct, and you could use it to make heterogeneously aggregated data structures that had members. The key thing to know about C is that when you have a struct called currentUser, and a member like id, and you ...

extension methods In some programming languages, there is a style of “monkey-patching” classes in order to add convenience methods. For example, let’s say that we’re using Ruby on Rails, and we have an array called chain_of_command. Although Ruby’s Array class does not define a special method for ob...

We’ve previously looked at using ES.later method decorators like this:1 const wrapWith = (decorator) => function (target, name, descriptor) { descriptor.value = decorator(descriptor.value); } const fluent = (method) => function (...args) { method.apply(this, args); return this; } class Person { @wra...

Writing higher-order functions in JavaScript is a long-established practice: A higher-order function is a function that takes one or more functions as arguments, returns a function, or both. For example, compose is a higher-order function that takes two functions as arguments, and returns a function...

In Functional Mixins, we discussed mixing functionality into JavaScript classes, changing the class. We observed that this has pitfalls when applied to a class that might already be in use elsewhere, but is perfectly cromulent when used as a technique to build a class from scratch. When used strictl...

In Functional Mixins, we discussed mixing functionality into JavaScript classes. The act of mixing functionality in changes the class. This approach maps well to idioms from other languages, such as Ruby’s modules. It also helps us decompose classes into smaller entities with focused responsibilitie...

In Prototypes are Objects, we saw that you can emulate “mixins” using Object.assign on the prototypes that underly JavaScript “classes.” We’ll revisit this subject now and spend more time looking at mixing functionality into classes. First, a quick recap: In JavaScript, a “class” is implemented as a...

Prerequisite: This post presumes that readers are familiar with JavaScript’s objects, know how a prototype defines behaviour for an object, know what a constructor function is, and how a constructor’s .prototype property is related to the objects it constructs. Passing familiarity with ECMAScript 20...

Prerequisite: This post presumes that readers are familiar with JavaScript’s objects, know how a prototype defines behaviour for an object, know what a constructor function is, and how a constructor’s .prototype property is related to the objects it constructs. Passing familiarity with ECMAScript 20...

Disclaimer: JavaScript the language has some complicated edge cases, and as such, the following essay has some hand-wavey bits and some bits that are usually correct but wrong for certain edge cases. If it helps any, pretend that nearly every statement has a footnote reading, “for most cases in prac...

Programming with objects and classes began in Norway in the late 1960s with the Simula programming language. Its creators, Ole-Johan Dahl and Kristen Nygaard, did not use those words to describe what would eventually become the dominant paradigm in computing. A decade later, Dr. Alan Kay coined the ...

Programmers love to discuss interviewing programmers. And hate to discuss it. Interviewing touches the very heart of human social interaction: It’s a process for picking “winners” and “losers,” for determining who’s “in” and who’s “out.” Today I’d like to discuss an anti-pattern, Carnac the Magnific...

(This material originally appeared, using ECMAScript-5 semantics, in 2013.) Dr. Hilbert “Bertie” David grows tired of blogging about JavaScript, and decides to cash in on the seemingly inexhaustible supply of impressionable young minds seeking to “Learn JavaScript in Five Days.” He opens his Grand J...

A variadic function is designed to accept a variable number of arguments.1 In JavaScript, you can make a variadic function by gathering parameters. For example: const abccc = (a, b, ...c) => { console.log(a); console.log(b); console.log(c); }; abccc(1, 2, 3, 4, 5) 1 2 [3,4,5] This can be useful when...

Some of this material originally appeared in What’s the difference between Currying and Partial Application? Here it is again, in ECMAScript 2015 syntax. What is Partial Application? Good question! arity Before we jump in, let’s get some terminology straight. Functions have arity, meaning the number...

In JavaScript, functions are first-class entities: You can store them in data structures, pass them to other functions, and return them from functions. An amazing number of very strong programming techniques arise as a consequence of functions-as-first-class-entities. One of the strongest is also on...