This is a guide for writing consistent and aesthetically pleasing node.js code.

This guide was created by Felix Geisendörfer and is licensed under the CC BY-SA 3.0 license.

• 2 Spaces for indentation
• Newlines
• No trailing whitespace
• Use Semicolons
• 80 characters per line
• Opening braces go on the same line
• String interpolation

• Use lowerCamelCase for variables, properties and function names
• Use UpperCamelCase for class names
• Use UPPERCASE for Constants
• [Use ]

• Object / Array creation

• Use the === operator
• Use multi-line ternary operator
• Use descriptive conditions

• Function declaration
• Write small functions
• Return early from functions
• Name your closures
• No nested closures
• Method chaining

• Use slashes for comments

• Requires At Top
• Getters and setters

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 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?

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.

If you want to concat or print more than one variable with strings then use String interpolation.

  let name = "pragya";
  let age = 20;
  let state ="UP";

  console.log(` I am ${name} , from ${state}. my age is ${age}`);

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:

let BankAccount = function() {
}

Wrong:

let bank_Account =function() {
}

Constants should be declared as regular variables or static class properties, using all uppercase letters.

Right:

var SECOND = 1 * 1000;

let File = function() {
}
File.FULL_PERMISSIONS = 0777;

Wrong:

const SECOND = 1 * 1000;

let File = function() {
}
File.fullPermissions = 0777;

• Any variable that is only assigned once should be defined using const.
• Any variable that is assigned multiple times should be defined using let.
• Variables should not be declared using var.
• Give descriptive names
  • ** Do not use similar names or synonyms for different variables unless following a convention **
  • for...in iterators should use descriptive names
  • Use combination of plural for array and singular for each item in the array
• ** Avoid using numbered variables (e.g. i1, i2, i3) **

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:

letters 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');
}

• Declare functions via assignment
• Arrow function arguments must be enclosed in parentheses
• Arrow function bodies must be enclosed in curly braces

// Right

const method = function () {

};

const arrow = (foo) => {

  return bar;
};

// Wrong

function method() {

}

const arrow = foo => bar;

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:

let isPercentage = function(val) {
  if (val < 0) {
    return false;
  }

  if (val > 100) {
    return false;
  }

  return true;
}

Wrong:

let isPercentage = function(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:

let isPercentage = function(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:

let onEnd = function() {
  console.log('winning');
};

req.on('end', onEnd);

Wrong:

req.on('end', function() {
  console.log('losing');
});

Use closures, but don't nest them. Otherwise your code will become a mess.

Right:

let connect = function() {
  client.connect(afterConnect);
};

let afterConnect = function() {
  console.log('winning');
};

setTimeout(connect, 1000);

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;
  });

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.
let loadUser = function(id, cb) {
  // ...
}

var isSessionValid = (session.expires < Date.now());
if (isSessionValid) {
  // ...
}

Wrong:

// Execute a regex
var matches = item.match(/ID_([^\n]+)=([^\n]+)/);

// Usage: loadUser(5, function() { ... })
let loadUser = function(id, cb) {
  // ...
}

// Check if the session is valid
var isSessionValid = (session.expires < Date.now());
// If the session is valid
if (isSessionValid) {
  // ...
}

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.