This is a collection of style guides for Kibana projects. The include guides for the following:
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.
Try to limit your lines to 80 characters. If it feels right, you can go up to 120 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');
}Also, notice the use of whitespace before and after the condition statement.
Right:
if (err) {
return cb(err);
}Wrong:
if (err)
return cb(err);But single-line conditionals are allowed for short lines
Preferred:
if (err) {
return cb(err);
}Allowed:
if (err) return cb(err);Declare one variable per var 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:
var keys = ['foo', 'bar'];
var values = [23, 42];
var object = {};
while (keys.length) {
var 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:
var adminUser = db.query('SELECT * FROM users ...');Wrong:
var 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.
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;These are numbers (or other values) simply used in line in your code. Do not use these, give them a variable name so they can be understood and changed easily.
Right:
var minWidth = 300;
if (width < minWidth) {
...
}Wrong:
if (width < 300) {
...
}Don't do this. Everything should be wrapped in a module that can be depended on by other modules. Even things as simple as a single value should be a module.
Prefer the use of function declarations over function expressions. Function expressions are allowed, but should usually be avoided.
Also, keep function definitions above other code instead of relying on function hoisting.
Preferred:
function myFunc() {
...
}Allowed:
var myFunc = function () {
...
};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'
};Use native ES5 methods to iterate and transform arrays and objects where possible. Do not use for and while loops.
Use descriptive variable names in the closures.
Use a utility library as needed and where it will make code more comprehensible.
Right:
var userNames = users.map(function (user) {
return user.name;
});
// examples where lodash makes the code more readable
var userNames = _.pluck(users, 'name');Wrong:
var userNames = [];
for (var i = 0; i < users.length; i++) {
userNames.push(users[i].name);
}Programming is not about remembering stupid rules. Use the triple equality operator as it will work just as expected.
Right:
var a = 0;
if (a !== '') {
console.log('winning');
}Wrong:
var a = 0;
if (a == '') {
console.log('losing');
}And never use multiple ternaries together
Right:
var foo = (a === b) ? 1 : 2;Wrong:
var foo = (a === b) ? 1 : (a === c) ? 2 : 3;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');
}Any non-trivial conditions should be assigned to a descriptively named variables, broken into several names variables, or converted to be a function:
Right:
var thing = ...;
var isShape = thing instanceof Shape;
var notSquare = !(thing instanceof Square);
var largerThan10 = isShape && thing.size > 10;
if (isShape && notSquare && largerThan10) {
console.log('some big polygon');
}Wrong:
if (
thing instanceof Shape
&& !(thing instanceof Square)
&& thing.size > 10
) {
console.log('bigger than ten?? Woah!');
}Right:
var validPasswordRE = /^(?=.*\d).{4,}$/;
if (password.length >= 4 && validPasswordRE.test(password)) {
console.log('password is valid');
}Wrong:
if (password.length >= 4 && /^(?=.*\d).{4,}$/.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 ~15 lines of code per function.
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;
}When using a chaining syntax (jquery or promises, for example), do not indent the subsequent chained operations, unless there is a logical grouping in them.
Also, if the chain is long, each method should be on a new line.
Right:
$('.someClass')
.addClass('another-class')
.append(someElement)d3.selectAll('g.bar')
.enter()
.append('thing')
.data(anything)
.exit()
.each(function() ... )Wrong:
$('.someClass')
.addClass('another-class')
.append(someElement)d3.selectAll('g.bar')
.enter().append('thing').data(anything).exit()
.each(function() ... )Feel free to give your closures a descriptive 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);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.
Exception: Comment blocks describing a function and it's arguments (docblock) should start with /**, contain a single * at the begining of each line, and end with */.
Right:
// 'ID_SOMETHING=VALUE' -> ['ID_SOMETHING=VALUE', 'SOMETHING', 'VALUE']
var matches = item.match(/ID_([^\n]+)=([^\n]+)/));
/**
* Fetches a user from...
* @param {string} id - id of the user
* @return {Promise}
*/
function loadUser(id) {
// 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.
...
}
var 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) {
// ...
}We use a version management system. If a line of code is no longer needed, remove it, don't simply comment it out.
While JavaScript it is not always considered an object-oriented language, it does have the building blocks for writing object oriented code. Of course, as with all things JavaScript, there are many ways this can be accomplished. Generally, we try to err on the side of readability.
When Defining a Class/Constructor, use the function definition syntax.
Right:
function ClassName() {
}Wrong:
var ClassName = function () {};While you can do it with pure JS, a utility will remove a lot of boilerplate, and be more readable and functional.
Right:
// uses a lodash inherits mixin
// inheritance is defined first - it's easier to read and the function will be hoisted
_.class(Square).inherits(Shape);
function Square(width, height) {
Square.Super.call(this);
}Wrong:
function Square(width, height) {
this.width = width;
this.height = height;
}
Square.prototype = Object.create(Shape);It is often the case that there are properties that can't be defined on the prototype, or work that needs to be done to completely create an object (like call it's Super class). This is all that should be done within constructors.
Try to follow the Write small functions rule here too.
If a method/property can go on the prototype, it probably should.
function Square() {
...
}
/**
* method does stuff
* @return {undefined}
*/
Square.prototype.method = function () {
...
}When creating a prototyped class, each method should almost always start with:
var self = this;
With the exception of very short methods (roughly 3 lines or less), self should always be used in place of this.
Avoid the use of bind
Right:
Square.prototype.doFancyThings = function () {
var self = this;
somePromiseUtil()
.then(function (result) {
self.prop = result.prop;
});
}Wrong:
Square.prototype.doFancyThings = function () {
somePromiseUtil()
.then(function (result) {
this.prop = result.prop;
}).bind(this);
}Allowed:
Square.prototype.area = function () {
return this.width * this.height;
}Crazy shit that you will probably never need. Stay away from it.
Feel free to use getters that are free from side effects, like providing a length property for a collection class.
Do not use setters, they cause more problems for people who try to use your software than they can solve.
Things listed here are specific to Kibana and likely only apply to this project
When creating a utility function, attach it as a lodash mixin.
Several already exist, and can be found in src/kibana/utils/_mixins.js
Kibana uses AMD modules to organize code, and require.js to load those modules.
Even Angular code is loaded this way.
Paths to modules should not be relative (ie. no dot notation). Instead, they should be loaded from one of the defined paths in the require config.
Right:
require('some/base/path/my_module');
require('another/path/another_module');Wrong:
require('../my_module');
require('./path/another_module');Module dependencies should be loaded via the CommonJS syntax:
Right:
define(function (require) {
var _ = require('lodash');
...
});Wrong:
define(['lodash'], function (_) {
...
});Kibana is written in Angular, and uses several utility methods to make using Angular easier.
Angular modules are defined using a custom require module named module. It is used as follows:
var app = require('ui/modules').get('app/namespace');app above is a reference to an Angular module, and can be used to define controllers, providers and anything else used in Angular.
A service called Private is available to load any function as an angular module without needing to define it as such. It is used as follows:
app.controller('myController', function($scope, otherDeps, Private) {
var ExternalClass = Private(require('path/to/some/class'));
...
});A more robust version of Angular's $q service is available as Promise. It can be used in the same way as $q, but it comes packaged with several utility methods that provide many of the same useful utilities as Bluebird.
app.service('CustomService', function(Promise, otherDeps) {
new Promise(function (resolve, reject) {
...
});
var promisedFunc = Promise.cast(someFunc);
return Promise.resolve('value');
});Angular routes are defined using a custom require modules named routes that remove much of the required boilerplate.
require('ui/routes')
.when('/my/object/route/:id?', {
// angular route code goes here
});This JavaScript guide forked from the node style guide created by Felix Geisendörfer and is licensed under the CC BY-SA 3.0 license.