This is a guide for writing consistent and aesthetically pleasing JavaScript. It is inspired by what is popular within the community, and flavored with some personal opinions.
$ npm install crispy
$ ./node_modules/crispy/node_modules/.bin/eslint -c ./node_modules/crispy/.eslintrc ./lib/ ./test/
Use 4 spaces for indenting your code and swear an oath to never mix tabs and spaces—a special kind of hell is awaiting you otherwise.
Use UNIX-style newlines (\n
), and a newline character as the last character
of a file. Windows-style newlines (\r\n
) are forbidden inside any repository.
Just like you brush your teeth after every meal, you clean up any trailing whitespace in your JS files before committing. Otherwise the rotten smell of careless neglect will eventually drive away contributors and/or co-workers.
There are rare occasions where you need a semicolon. Read about them here.
Limit your lines to 80 characters. Yes, screens have gotten much bigger over the last few years, but your brain has not. Use the additional room for split screen, your editor supports that, right? And increase the font size so your colleague standing behind can read it too.
Use single quotes, unless you're writing JSON.
Right:
var foo = 'bar'
Wrong:
var foo = "bar"
Your opening braces go on the same line as the statement.
Right:
if (true) {
console.log('winning')
}
Wrong:
if (true)
{
console.log('losing')
}
Also, notice the use of whitespace before and after the condition statement.
Declare one variable per var statement, it makes it easier to re-order the lines. Put them at the beginning of the function body.
Right:
var keys = ['foo', 'bar']
var values = [23, 42]
var object = {}
var key
while (items.length) {
key = keys.pop()
object[key] = values.pop()
}
Wrong:
var keys = ['foo', 'bar'],
values = [23, 42],
object = {},
key;
while (items.length) {
key = keys.pop()
object[key] = values.pop()
}
Variables, properties and function names should use lowerCamelCase
. They should also be descriptive. Single character variables and uncommon abbreviations should generally be avoided.
Right:
var adminUser = db.query('SELECT * FROM users ...')
Wrong:
var admin_user = db.query('SELECT * FROM users ...')
Class names should be capitalized using UpperCamelCase
.
Right:
function BankAccount() {}
Wrong:
function bank_Account() {}
Constants should be declared as regular variables or static class properties, using all uppercase letters.
Node.js/V8 actually supports mozilla's const extension, but unfortunately that cannot be applied to class members, nor is it part of any ECMA standard.
Right:
var SECOND = 1 * 1000
function File() {}
File.FULL_PERMISSIONS = 0777
Wrong:
const SECOND = 1 * 1000
function File() {}
File.fullPermissions = 0777
Use trailing commas and put short declarations on a single line. Only quote keys when your interpreter complains:
Right:
var a = ['hello', 'world']
var b = {
good: 'code',
'is generally': 'pretty'
}
Wrong:
var a = [
'hello', 'world'
]
var b = {"good": 'code'
, is generally: 'pretty'
}
Programming is not about remembering stupid rules. Use the triple equality operator as it will work just as expected.
Right:
var a = 0
if (a === '') {
console.log('winning')
}
Wrong:
var a = 0
if (a == '') {
console.log('losing')
}
The ternary operator should not be used on a single line. Split it up into multiple lines instead.
Right:
var foo = (a === b)
? 1
: 2
Wrong:
var foo = (a === b) ? 1 : 2
Do not extend the prototype of native JavaScript objects. Your future self will be forever grateful.
Right:
var a = []
if (!a.length) {
console.log('winning')
}
Wrong:
Array.prototype.empty = function() {
return !this.length
}
var a = []
if (a.empty()) {
console.log('losing')
}
Any non-trivial conditions should be assigned to a descriptive variable:
Right:
var isAuthorized = (user.isAdmin() || user.isModerator())
if (isAuthorized) {
console.log('winning')
}
Wrong:
if (user.isAdmin() || user.isModerator()) {
console.log('losing')
}
Keep your functions short. A good function fits on a slide that the people in the last row of a big room can comfortably read. So don't count on them having perfect vision and limit yourself to ~15 lines of code per function.
To avoid deep nesting of if-statements, always return a function's value as early as possible.
Right:
function isPercentage(val) {
if (val < 0) return false
if (val > 100) return false
return true
}
Wrong:
function isPercentage(val) {
if (val >= 0) {
if (val < 100) {
return true;
} else {
return false;
}
} else {
return false;
}
}
Use closures, but try not to nest them. Otherwise your code will become a mess.
Right:
setTimeout(function() {
client.connect(afterConnect)
}, 1e3)
function afterConnect() {
console.log('winning')
}
Wrong:
setTimeout(function() {
client.connect(function() {
console.log('losing')
})
}, 1e3)
isaacs posted a nice explanation here.
Right:
function myAsyncFn(stuff, callback) {
if (!stuff) {
return process.nextTick(function(){
return callback(new Error('stuff is undefined'))
})
}
return doSomeSlowStuff(stuff, callback)
}
Wrong:
function myAsyncFn(stuff, callback) {
if (!stuff) {
return callback(new Error('stuff is undefined')) // Sometimes returns now...
}
return doSomeSlowStuff(stuff, callback) // Other times returns later
}
Crazy shit that you will probably never need. Stay away from it.
MIT, see LICENSE for details.
The original version of this guide was created by Felix Geisendörfer.