angelogeminiani / pragmatic.js

Pragmatic rules for writing JavaScript

Pragmatic.js code style guidelines

TL;DR

General coding:

• Use long, descriptive variable and method names
• Use blank lines to separate "paragraphs" of code for readability
• Use comments to describe non-obvious code behavior
• Don't write comments that do not add to code understanding
• Optimize for performance only if there's a measurable problem
• If a source file is longer than 200 LoC, it's time to split it up

Functions:

• Use one var statement per function, at the top
• function name() { } for named functions
• function(){ } for anonymous functions
• Don't use more than 10 LoC per method (except for closures)

Statements & expressions:

• Use short and concise expressions
• Use duck-typing and rely on unit tests rather than testing for types of arguments
• Prefer functional programming over for and while loops
• No curly braces for single-line control flow statements such as if & friends
• Don't write semicolons that are optional
• Put a single semicolon before statements that start with ( or [ (see above article as for why it's needed)
• Use ternary when it is simple enough as to not make code difficult to understand
• Do not use try and catch unless absolutely required (like an API forcing you to do so)

Pragmatic JavaScript

The word pragmatic means "Practical, concerned with making decisions and actions that are useful in practice, not just theory."1 Writing pragmatic JavaScript is all about optimizing the process of writing JavaScript for you as a programmer, using all the facilities the language provides.

Writing less code is good; emphasized by the no optional semicolons rule, by no curly braces where not necessary and by using functional programming constructs whereever possible.

At the same time, when you come back to your code later, you want to understand it— thus long, descriptive variable and method names, and comments where necessary.

JavaScript is a modern, flexible and malleable scripting language, and it deserves to be treated as such. Pragmatic.js is also about discovering and learning the language strengths as well as its quirks so you can make full use of it.

Examples

Here are some examples from Zepto.js.

// typical helper function
function eachEvent(events, fn, iterator){
  if ($.isObject(events)) $.each(events, iterator)
  else events.split(/\s/).forEach(function(type){ iterator(type, fn) })
}

// shortcut methods for `.bind(event, fn)` for each event type
;('focusin focusout load resize scroll unload click dblclick '+
'mousedown mouseup mousemove mouseover mouseout '+
'change select keydown keypress keyup error').split(' ').forEach(function(event) {
  $.fn[event] = function(callback){ return this.bind(event, callback) }
})

// from Zepto core, $.fn.siblings implementation
function filtered(nodes, selector) {
  return selector === undefined ? $(nodes) : $(nodes).filter(selector)
}

$.fn.siblings = function(selector){
  return filtered(this.map(function(i, el){
    return slice.call(el.parentNode.children).filter(function(child){ return child!==el })
  }), selector)
}

Contribute

I welcome contributions—this guide is very basic at the moment and should probably have some more guidelines for specific situations and how to get started. You know where the fork & pull request buttons are.

License

Pragmatic.js is licensed under the terms of the MIT License.