This is a guide for writing consistent and aesthetically pleasing node.js code. It is inspired by what is popular within the community, and flavored with some personal opinions.
There is a .jshintrc which enforces these rules as closely as possible. You can either use that and adjust it, or use this script to make your own.
This guide was created by Felix Geisendörfer and is licensed under the CC BY-SA 3.0 license. You are encouraged to fork this repository and make adjustments according to your preferences.
- 2 Spaces for indentation
- Newlines
- No trailing whitespace
- Use Semicolons
- 80 characters per line
- Use single quotes
- Opening braces go on the same line
- Declare one variable per let statement
- Use lowerCamelCase for variables, properties and function names
- Use UpperCamelCase for class names
- Use UPPERCASE for Constants
- Write small functions
- Return early from functions
- Name your closures
- No nested closures
- Method chaining
- Object.freeze, Object.preventExtensions, Object.seal, with, eval
- Requires 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 Node.js Style Guide .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 be a traditionalist when it comes to abusing error correction mechanisms for cheap syntactic pleasures.
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?
Use single quotes, unless you are writing JSON.
Right:
let foo = 'bar';Wrong:
let 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 let statement, 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:
let keys = ['foo', 'bar'];
let values = [23, 42];
let object = {};
while (keys.length) {
let key = keys.pop();
object[key] = values.pop();
}Wrong:
let 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:
let adminUser = db.query('SELECT * FROM users ...');Wrong:
let admin_user = db.query('SELECT * FROM users ...');Class names should be capitalized using UpperCamelCase.
Right:
const BankAccount = () => {
}Wrong:
const bank_Account = () => {
}Constants should be declared as regular variables or static class properties, using all uppercase letters.
Right:
let SECOND = 1 * 1000;
const File() => {
}
File.FULL_PERMISSIONS = 0777;Wrong:
const SECOND = 1 * 1000;
const File = () => {
}
File.fullPermissions = 0777;Use trailing commas and put short declarations on a single line. Only quote keys when your interpreter complains:
Right:
let a = ['hello', 'world'];
let b = {
good: 'code',
'is generally': 'pretty',
};Wrong:
let a = [
'hello', 'world'
];
let 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:
let a = 0;
if (a !== '') {
console.log('winning');
}Wrong:
let 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:
let foo = (a === b)
? 1
: 2;Wrong:
let foo = (a === b) ? 1 : 2;Any non-trivial conditions should be assigned to a descriptively named variable or function:
Right:
let 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');
}Exporting variables, functions, or classes from a file can be achieved in a couple different ways in ES6. A couple sceneraios you will encounter are below.
// FILE 1
const add = (a, b) => {
return a + b;
}
const subtract = (a, b) => {
return a - b;
}
export { add, substract }// FILE 1
export const add = (a, b) => {
return a + b;
}
export const subtract = (a, b) => {
return a - b;
}Importing from the examples above is done as below:
// FILE 2
import { add, subtract } from './file1.js'When exporting a single item from a file it is cleaner to use a default export. It is not recommended to export default an anonymous function.
// FILE 1
export default function isTall(inches){
return inches > 72
}function isTall(inches){
return inchex > 72
}
export default isTall;Importing from the examples above looks like this. Notice this is way cleaner.
// FILE 2
import isTall from './file1.js'export const add = (a, b) => {
return a + b;
}
export const subtract = (a, b) =>{
return a - b;
}
export const multiply = (a, b) => {
return a * b;
}
export const divide = (a, b) => {
return a / b;
}
const Math = {add, subtract, multiply, divide};
export default Math;Importing from the example above looks like this.
// FILE 2
import Math, { add } from './file1.js'
// Using the functions
Math.multiply(1,2);
add.(1,2);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.
as possible.
Right:
const isPercentage = (val) => {
if (val < 0) {
return false;
}
if (val > 100) {
return false;
}
return true;
}Wrong:
const 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:
const isPercentage = (val) => {
let 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', onEnd);
const onEnd = () => {
console.log('winning');
}Wrong:
req.on('end', () => {
console.log('losing');
});Use closures, but don't nest them. Otherwise your code will become a mess.
Right:
setTimeout(() => {
client.connect(afterConnect);
}, 1000);
const afterConnect = () => {
console.log('winning');
}Wrong:
setTimeout(() => {
client.connect(() => {
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((err, user) => {
return true;
});Wrong:
User
.findOne({ name: 'foo' })
.populate('bar')
.exec((err, user) => {
return true;
});
User.findOne({ name: 'foo' })
.populate('bar')
.exec((err, user) => {
return true;
});
User.findOne({ name: 'foo' }).populate('bar')
.exec((err, user) => {
return true;
});
User.findOne({ name: 'foo' }).populate('bar')
.exec((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']
let 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.
const loadUser = (id, cb) => {
// ...
}
let isSessionValid = (session.expires < Date.now());
if (isSessionValid) {
// ...
}Wrong:
// Execute a regex
let matches = item.match(/ID_([^\n]+)=([^\n]+)/);
// Usage: loadUser(5, () => { ... })
const loadUser = (id, cb) => {
// ...
}
// Check if the session is valid
let 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 requires 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.
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:
let a = [];
if (!a.length) {
console.log('winning');
}Wrong:
Array.prototype.empty = () => {
return !this.length;
}
let a = [];
if (a.empty()) {
console.log('losing');
}