This is a guide for writing consistent and aesthetically pleasing node.js code.
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.
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 1 tab 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.
The usage of semicolons used to be a core value of JS and is no longer need.
Limit your lines to 80 characters.
Use single quotes, unless you are 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');
}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. If declaring multiple empty variables at the head of your js page, it's better to declare them as a group if they will be related to one another.
Right:
let keys = ['foo', 'bar']
let values = [23, 42]
let dog, cat, horse, cow, pig, wolf
let object = {}
while (keys.length) {
let key = keys.pop()
object[key] = values.pop()
}Wrong:
var 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:
var admin_user = db.query('SELECT * FROM users ...');Don't 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:
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:
let 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:
let foo = (a === b)
? 1
: 2;Wrong:
var 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');
}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 ~20 lines of code per function.
To avoid deep nesting of if-statements, always return a function's value as early as possible.
Right:
let 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) {
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', 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']
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.
function loadUser(id, cb) {
// ...
}
let isSessionValid = (session.expires < Date.now());
if (isSessionValid) {
// ...
}Wrong:
// Execute a regex
var matches = item.match(/ID_([^\n]+)=([^\n]+)/);
// Usage: loadUser(5, function() { ... })
function loadUser(id, cb) {
// ...
}
// Check if the session is valid
var 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. Be sure to use const for any requires.
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 = function() {
return !this.length;
}
var a = [];
if (a.empty()) {
console.log('losing');
}