This style guide is based on https://github.com/felixge/node-style-guide and adapted for our needs.
- 2 Spaces for indentation
- Newlines
- No trailing whitespace
- Use Semicolons
- 100 characters per line
- Use single quotes
- Opening braces go on the same line
- Declare one variable per declaration and initialization
- Use lowerCamelCase for variables, properties and function names
- Use UpperCamelCase for class names
- Use UPPERCASE for Constants
- Other notes for naming conventions
- Object.freeze, Object.preventExtensions, Object.seal, with, eval
- Modules imports at top
- Getters and setters
- Do not extend built-in prototypes
You may want to use editorconfig.org to enforce the formatting settings in your editor. Use the .editorconfig file to have indentation, newslines and whitespace behavior automatically set to the rules set up below.
Use 2 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.
According to scientific research, the usage of semicolons is a core value of our community. Consider the points of the opposition, but be a traditionalist when it comes to abusing error correction mechanisms for cheap syntactic pleasures.
Limit your lines to 100 characters.
Use single quotes, unless you are writing JSON.
Right:
const foo = 'bar';Wrong:
const 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 declaration and initialization, it makes it easier to re-order the lines. However, ignore Crockford when it comes to declaring variables deeper inside a function, just put the declarations wherever they make sense.
Right:
const keys = ['foo', 'bar'];
const values = [23, 42];
const object = {};
while (keys.length) {
const key = keys.pop();
object[key] = values.pop();
}Wrong:
const keys = ['foo', 'bar'],
values = [23, 42],
object = {},
key;
while (keys.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:
const adminUser = db.query('SELECT * FROM users ...');Wrong:
const 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.
Right:
let SECOND = 1 * 1000;
function File() {
}
File.FULL_PERMISSIONS = 0777;Wrong:
const SECOND = 1 * 1000;
function File() {
}
File.fullPermissions = 0777;Read 'Naming convention' page on Confluence
Use trailing commas and put short declarations on a single line. Only quote keys when your interpreter complains:
Right:
const a = ['hello', 'world'];
const b = {
good: 'code',
'is generally': 'pretty',
};Wrong:
const a = [
'hello', 'world'
];
const 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:
const a = 0;
if (a !== '') {
console.log('winning');
}Wrong:
const a = 0;
if (a == '') {
console.log('losing');
}Any non-trivial conditions should be assigned to a descriptively named variable or function:
Right:
const isValidPassword = password.length >= 4 && /^(?=.*\d).{4,}$/.test(password);
if (isValidPassword) {
console.log('winning');
}Wrong:
if (password.length >= 4 && /^(?=.*\d).{4,}$/.test(password)) {
console.log('losing');
}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;
}
}Or for this particular example it may also be fine to shorten things even further:
function isPercentage(val) {
const isInRange = (val >= 0 && val <= 100);
return isInRange;
}Feel free to give your closures a name. It shows that you care about them, and will produce better stack traces, heap and cpu profiles.
Right:
req.on('end', function onEnd() {
console.log('winning');
});Wrong:
req.on('end', function() {
console.log('losing');
});Use closures, but don't nest them. Otherwise your code will become a mess.
Right:
setTimeout(function() {
client.connect(afterConnect);
}, 1000);
function afterConnect() {
console.log('winning');
}Wrong:
setTimeout(function() {
client.connect(function() {
console.log('losing');
});
}, 1000);One method per line should be used if you want to chain methods.
You should also indent these methods so it's easier to tell they are part of the same chain.
Right:
User
.findOne({ name: 'foo' })
.populate('bar')
.exec(function(err, user) {
return true;
});Wrong:
User
.findOne({ name: 'foo' })
.populate('bar')
.exec(function(err, user) {
return true;
});
User.findOne({ name: 'foo' })
.populate('bar')
.exec(function(err, user) {
return true;
});
User.findOne({ name: 'foo' }).populate('bar')
.exec(function(err, user) {
return true;
});
User.findOne({ name: 'foo' }).populate('bar')
.exec(function(err, user) {
return true;
});Use slashes for both single line and multi line comments. Try to write comments that explain higher level mechanisms or clarify difficult segments of your code. Don't use comments to restate trivial things.
Right:
// 'ID_SOMETHING=VALUE' -> ['ID_SOMETHING=VALUE', 'SOMETHING', 'VALUE']
const matches = item.match(/ID_([^\n]+)=([^\n]+)/));
// This function has a nasty side effect where a failure to increment a
// redis counter used for statistics will cause an exception. This needs
// to be fixed in a later iteration.
function loadUser(id, cb) {
// ...
}
const isSessionValid = (session.expires < Date.now());
if (isSessionValid) {
// ...
}Wrong:
// Execute a regex
const matches = item.match(/ID_([^\n]+)=([^\n]+)/);
// Usage: loadUser(5, function() { ... })
function loadUser(id, cb) {
// ...
}
// Check if the session is valid
const isSessionValid = (session.expires < Date.now());
// If the session is valid
if (isSessionValid) {
// ...
}Crazy shit that you will probably never need. Stay away from it.
Always put modules imports at top of file to clearly illustrate a file's dependencies. Besides giving an overview for others at a quick glance of dependencies and possible memory impact, it allows one to determine if they need a package.json file should they choose to use the file elsewhere.
Right:
import firstModule from './firstModule.js';
import secondModule from './secondModule.js';
const SOME_CONSTANT = 'some-constant';
function main() {
//
// ...
//
}Wrong:
const SOME_CONSTANT = 'some-constant';
import firstModule from './firstModule.js';
function main() {
//
// ...
//
}
import secondModule from './secondModule.js';Do not use setters, they cause more problems for people who try to use your software than they can solve.
Feel free to use getters that are free from side effects, like providing a length property for a collection class.
Do not extend the prototype of native JavaScript objects. Your future self will be forever grateful.
Right:
const a = [];
if (!a.length) {
console.log('winning');
}Wrong:
Array.prototype.empty = function() {
return !this.length;
}
const a = [];
if (a.empty()) {
console.log('losing');
}