Javascript Style Guide

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.

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.

This version is updated by Mark Sergienko for use within MethodExists Inc.

2 Spaces for indention

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. No Exceptions.

Newlines

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.

No trailing whitespace

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.

Use Semicolons

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.

80 characters per line

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 double quotes

Right:

var foo = "bar";

Opening braces go on the same line

Your opening braces go on the same line as the statement.

Right:

if(true) {
  console.log("winning");
}

Wrong:

if(true)
{
  console.log("losing");
}

Spacing

Spacing around curly braces:

Wrong:

}catch(err){

try{

return function(params, session){

if(!_.isFalsey(profile)){

}else{

Right:

} catch(err) {

try {

return function(params, session) {

if( !_.isFalsey(profile) ) { 

} else {

Spacing around parentheses ( ):

If condition inside if, switch or elsewhere is rather simple, no spaces required. Spaces right after ( and before ) are required for more complex conditions:

if(param) {
  something;
}

// or:
if( param && !yetSet ) {
  somethingElse;
}

Variable definition blocks

You can make var statement with multiple var once per closure or module, on top of it. Here are some examples:

Right:

var lib = require("./lib"),
    _ = require("platform2/shared/functional");

Do NOT line up = signs

Do NOT add extra spaces after var

Wrong:

var   _               = require("platform2/shared/functional"),
      saveProfile     = require("./saveProfile");

Use lowerCamelCase for variables, properties and function names

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 ...");

Use UpperCamelCase for class names

Class names should be capitalized using UpperCamelCase.

Right:

function BankAccount() {
}

Wrong:

function bank_Account() {
}

Use UPPERCASE for Constants

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;

Object / Array creation

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'
        };

Avoid excessive spacing:

return _.keys.all({

  categories: categories

});

Proper use of ternary operator

The ternary operator can be used on a single line if very simple. Otherwise, split it up into multiple lines instead.

Right:

var foo = (a === b) ? 
  long_expression : 
  another_long_expression;
// or:
var foo = (a === b) ? 1 : 2;

Do not extend built-in prototypes

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');
}

Use descriptive conditions

Any non-trivial conditions should be assigned to a descriptively named variable or function:

Right:

var 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");
}

Write small functions

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.

Return early from functions

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) {
  var isInRange = (val >= 0 && val <= 100);
  return isInRange;
}

Name your closures

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");
});

No nested closures

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

Right:

setTimeout(function connect() {
  client.connect(afterConnect);
}, 1000);

function afterConnect() {
  console.log("winning");
}

Wrong:

setTimeout(function() {
  client.connect(function() {
    console.log("losing");
  });
}, 1000);

Commenting

Use markdown multiline comments to describe major function or module:

/*
# viewActions
A lib for use in view.
View actions can be used in view events.

## Exports
{

## Todo
- Create the remove() function for removing items from arrays

*/

Use double slashes otherwise:

Wrong:

var self = this;
  /*
    We can pass another validator instead of schemata
  */
  
schemataValidator.build = function(dataModel){
    /* Build Actual schema Object */

Right:

      // copy context params to params key in viewConf
      viewConf.params = {};
      for(var paramKey in context.params) {
        if(!viewConf.params[paramKey] && _.isString(paramKey)) {
          viewConf.params[paramKey] = context.params[paramKey];
        }
      }

Try to describe easily what's happening in a condensed standalone block, but do not state obvious things:

Wrong:

//if there is username and password, concatenate it to connectin string
cn += (config.username && config.password) ? (config.username + ":" + config.password + "@") : "";

var getCollection = function(entity) {
  //return a collection
  return _db.collection(entity);
};
  

No creative comment banners:

Wrong:

  /**************************************************************************
   * ======      Functions
   **************************************************************************/

  // Main Process ==============================

Chaining

Put dots in the ends of the lines, not at the beginning!

Wrong:

return app.repo
    .select("fc_document")
    .filter({
      review_date: { ne: "" },
      owner: session.profile._id
    })
    .run();

Right:

return app.repo.
    select("fc_document").
    filter({
      review_date: { ne: "" },
      owner: session.profile._id
    }).
    run();

Splitting long chained lines

Splitting is allowed. Try to balance the lines, so that the beginning makes sense

Wrong:

// app is left meaningless:

directories: app.
      apiServer.callDataView("filingCabinetDirectoryDataView", params, session), 

Right:

directories: app.apiServer.
      callDataView("filingCabinetDirectoryDataView", params, session),

After the first next line and tab all the consequent chaining must be done on new line:

Wrong:

app.repo.
    select("fc_document”).filter({ }).
    run();

Right:

app.repo.
    select("fc_document").
    filter({ }).
    run();