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STYLEGUIDE.md
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This is a collection of style guides for Kibana projects. The include guides for the following:
- [JavaScript](#javascript-style-guide)
- [Kibana Project](#kibana-style-guide)
- [Html](#html-style-guide)
# JavaScript Style Guide
## 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.
## 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][hnsemicolons], 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.
[the opposition]: http://blog.izs.me/post/2353458699/an-open-letter-to-javascript-leaders-regarding
[hnsemicolons]: http://news.ycombinator.com/item?id=1547647
## 120 characters per line
Try to limit your lines to 80 characters. If it feels right, you can go up to 120 characters.
## Use single quotes
Use single quotes, unless you are writing JSON.
*Right:*
```js
var foo = 'bar';
```
*Wrong:*
```js
var foo = "bar";
```
## Opening braces go on the same line
Your opening braces go on the same line as the statement.
*Right:*
```js
if (true) {
console.log('winning');
}
```
*Wrong:*
```js
if (true)
{
console.log('losing');
}
```
Also, notice the use of whitespace before and after the condition statement.
## Always use braces for multi-line code
*Right:*
```js
if (err) {
return cb(err);
}
```
*Wrong:*
```js
if (err)
return cb(err);
```
## Prefer multi-line conditionals
But single-line conditionals are allowed for short lines
*Preferred:*
```js
if (err) {
return cb(err);
}
```
*Allowed:*
```js
if (err) return cb(err);
```
## Declare one variable per var statement
Declare one variable per var statement, it makes it easier to re-order the
lines. However, ignore [Crockford][crockfordconvention] when it comes to
declaring variables deeper inside a function, just put the declarations wherever
they make sense.
*Right:*
```js
var keys = ['foo', 'bar'];
var values = [23, 42];
var object = {};
while (keys.length) {
var key = keys.pop();
object[key] = values.pop();
}
```
*Wrong:*
```js
var keys = ['foo', 'bar'],
values = [23, 42],
object = {},
key;
while (keys.length) {
key = keys.pop();
object[key] = values.pop();
}
```
[crockfordconvention]: http://javascript.crockford.com/code.html
## 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:*
```js
var adminUser = db.query('SELECT * FROM users ...');
```
*Wrong:*
```js
var admin_user = db.query('SELECT * FROM users ...');
```
## Use UpperCamelCase for class names
Class names should be capitalized using `UpperCamelCase`.
*Right:*
```js
function BankAccount() {
}
```
*Wrong:*
```js
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][const] extension, but
unfortunately that cannot be applied to class members, nor is it part of any
ECMA standard.
*Right:*
```js
var SECOND = 1 * 1000;
function File() {
}
File.FULL_PERMISSIONS = 0777;
```
*Wrong:*
```js
const SECOND = 1 * 1000;
function File() {
}
File.fullPermissions = 0777;
```
[const]: https://developer.mozilla.org/en/JavaScript/Reference/Statements/const
## Magic numbers
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:*
```js
var minWidth = 300;
if (width < minWidth) {
...
}
```
*Wrong:*
```js
if (width < 300) {
...
}
```
## Global definitions
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.
## Function definitions
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:*
```js
function myFunc() {
...
}
```
*Allowed:*
```js
var myFunc = function () {
...
};
```
## Object / Array creation
Use trailing commas and put *short* declarations on a single line. Only quote
keys when your interpreter complains:
*Right:*
```js
var a = ['hello', 'world'];
var b = {
good: 'code',
'is generally': 'pretty'
};
```
*Wrong:*
```js
var a = [
'hello', 'world'
];
var b = {"good": 'code'
, is generally: 'pretty'
};
```
## Object / Array iterations, transformations and operations
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:*
```js
var userNames = users.map(function (user) {
return user.name;
});
// examples where lodash makes the code more readable
var userNames = _.pluck(users, 'name');
```
*Wrong:*
```js
var userNames = [];
for (var i = 0; i < users.length; i++) {
userNames.push(users[i].name);
}
```
## Use the === operator
Programming is not about remembering [stupid rules][comparisonoperators]. Use
the triple equality operator as it will work just as expected.
*Right:*
```js
var a = 0;
if (a !== '') {
console.log('winning');
}
```
*Wrong:*
```js
var a = 0;
if (a == '') {
console.log('losing');
}
```
[comparisonoperators]: https://developer.mozilla.org/en/JavaScript/Reference/Operators/Comparison_Operators
## Only use ternary operators for small, simple code
And **never** use multiple ternaries together
*Right:*
```js
var foo = (a === b) ? 1 : 2;
```
*Wrong:*
```js
var foo = (a === b) ? 1 : (a === c) ? 2 : 3;
```
## Do not extend built-in prototypes
Do not extend the prototype of native JavaScript objects. Your future self will
be forever grateful.
*Right:*
```js
var a = [];
if (!a.length) {
console.log('winning');
}
```
*Wrong:*
```js
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 variables, broken into
several names variables, or converted to be a function:
*Right:*
```js
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:*
```js
if (
thing instanceof Shape
&& !(thing instanceof Square)
&& thing.size > 10
) {
console.log('bigger than ten?? Woah!');
}
```
## Name regular expressions
*Right:*
```js
var validPasswordRE = /^(?=.*\d).{4,}$/;
if (password.length >= 4 && validPasswordRE.test(password)) {
console.log('password is valid');
}
```
*Wrong:*
```js
if (password.length >= 4 && /^(?=.*\d).{4,}$/.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:*
```js
function isPercentage(val) {
if (val < 0) return false;
if (val > 100) return false;
return true;
}
```
*Wrong:*
```js
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:
```js
function isPercentage(val) {
var isInRange = (val >= 0 && val <= 100);
return isInRange;
}
```
## Chaining operations
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:*
```js
$('.someClass')
.addClass('another-class')
.append(someElement)
```
```js
d3.selectAll('g.bar')
.enter()
.append('thing')
.data(anything)
.exit()
.each(function() ... )
```
```js
$http.get('/info')
.then(({ data }) => this.transfromInfo(data))
.then((transformed) => $http.post('/new-info', transformed))
.then(({ data }) => console.log(data));
```
*Wrong:*
```js
$('.someClass')
.addClass('another-class')
.append(someElement)
```
```js
d3.selectAll('g.bar')
.enter().append('thing').data(anything).exit()
.each(function() ... )
```
```js
$http.get('/info')
.then(({ data }) => this.transfromInfo(data))
.then((transformed) => $http.post('/new-info', transformed))
.then(({ data }) => console.log(data));
```
## Name your closures
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:*
```js
req.on('end', function onEnd() {
console.log('winning');
});
```
*Wrong:*
```js
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:*
```js
setTimeout(function() {
client.connect(afterConnect);
}, 1000);
function afterConnect() {
console.log('winning');
}
```
*Wrong:*
```js
setTimeout(function() {
client.connect(function() {
console.log('losing');
});
}, 1000);
```
## Use slashes for comments
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 its arguments (docblock) should start with `/**`, contain a single `*` at the beginning of each line, and end with `*/`.
*Right:*
```js
// '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:*
```js
// 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) {
// ...
}
```
## Do not comment out code
We use a version management system. If a line of code is no longer needed, remove it, don't simply comment it out.
## Classes/Constructors and Inheritance
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.
### Capitalized function definition as Constructors
When Defining a Class/Constructor, use the function definition syntax.
*Right:*
```js
function ClassName() {
}
```
*Wrong:*
```js
var ClassName = function () {};
```
### Inheritance should be done with a utility
While you can do it with pure JS, a utility will remove a lot of boilerplate, and be more readable and functional.
*Right:*
```js
// 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:*
```js
function Square(width, height) {
this.width = width;
this.height = height;
}
Square.prototype = Object.create(Shape);
```
### Keep Constructors Small
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 its Super class). This is all that should be done within constructors.
Try to follow the [Write small functions](#write-small-functions) rule here too.
### Use the prototype
If a method/property *can* go on the prototype, it probably should.
```js
function Square() {
...
}
/**
* method does stuff
* @return {undefined}
*/
Square.prototype.method = function () {
...
}
```
### Handling scope and aliasing `this`
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:*
```js
Square.prototype.doFancyThings = function () {
var self = this;
somePromiseUtil()
.then(function (result) {
self.prop = result.prop;
});
}
```
*Wrong:*
```js
Square.prototype.doFancyThings = function () {
somePromiseUtil()
.then(function (result) {
this.prop = result.prop;
}).bind(this);
}
```
*Allowed:*
```js
Square.prototype.area = function () {
return this.width * this.height;
}
```
## Object.freeze, Object.preventExtensions, Object.seal, with, eval
Crazy shit that you will probably never need. Stay away from it.
## Getters and Setters
Feel free to use getters that are free from [side effects][sideeffect], 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.
[sideeffect]: http://en.wikipedia.org/wiki/Side_effect_(computer_science)
- [JavaScript](https://github.com/elastic/kibana/style_guides/js_style_guide.md)
- [CSS](https://github.com/elastic/kibana/style_guides/css_style_guide.md)
- [HTML](https://github.com/elastic/kibana/style_guides/html_style_guide.md)
- [API](https://github.com/elastic/kibana/style_guides/api_style_guide.md)
# Kibana Style Guide
@ -866,59 +108,3 @@ require('ui/routes')
// angular route code goes here
});
```
# Html Style Guide
## Multiple attribute values
When a node has multiple attributes that would cause it to exceed the line character limit, each attribute including the first should be on its own line with a single indent. Also, when a node that is styled in this way has child nodes, there should be a blank line between the opening parent tag and the first child tag.
```
<ul
attribute1="value1"
attribute2="value2"
attribute3="value3">
<li></li>
<li></li>
...
</ul>
```
# Api Style Guide
## Paths
API routes must start with the `/api/` path segment, and should be followed by the plugin id if applicable:
*Right:* `/api/marvel/v1/nodes`
*Wrong:* `/marvel/api/v1/nodes`
## Versions
Kibana won't be supporting multiple API versions, so API's should not define a version.
*Right:* `/api/kibana/index_patterns`
*Wrong:* `/api/kibana/v1/index_patterns`
## snake_case
Kibana uses `snake_case` for the entire API, just like Elasticsearch. All urls, paths, query string parameters, values, and bodies should be `snake_case` formatted.
*Right:*
```
POST /api/kibana/index_patterns
{
"id": "...",
"time_field_name": "...",
"fields": [
...
]
}
```
# Attribution
This JavaScript guide forked from the [node style guide](https://github.com/felixge/node-style-guide) created by [Felix Geisendörfer](http://felixge.de/) and is
licensed under the [CC BY-SA 3.0](http://creativecommons.org/licenses/by-sa/3.0/)
license.

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# Api Style Guide
## Paths
API routes must start with the `/api/` path segment, and should be followed by the plugin id if applicable:
*Right:* `/api/marvel/v1/nodes`
*Wrong:* `/marvel/api/v1/nodes`
## Versions
Kibana won't be supporting multiple API versions, so API's should not define a version.
*Right:* `/api/kibana/index_patterns`
*Wrong:* `/api/kibana/v1/index_patterns`
## snake_case
Kibana uses `snake_case` for the entire API, just like Elasticsearch. All urls, paths, query string parameters, values, and bodies should be `snake_case` formatted.
*Right:*
```
POST /api/kibana/index_patterns
{
"id": "...",
"time_field_name": "...",
"fields": [
...
]
}
```

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# CSS Style Guide
## Concepts
### Think in terms of components
Think in terms of everything as a component: a button, a footer with buttons in
it, a list, a list item, the container around the list, the list title, etc.
Keep components as granular as possible.
Compose large, complex components out of smaller, simpler components.
### Introduce as little specificity as possible
Rules will need to overwrite other rules, and we can only do that via
specificity. For that reason, it's important to avoid introducing specificity
unless absolutely needed and that when we do so, we introduce as little as
possible.
## Quick reference
Here are some examples of how to structure your styles. The
rules that underly these examples are below.
```less
.kbButton {
padding: 5px;
border: 1px solid black;
/**
* 1. This button can appear in a "pressed" aka "pinned" state.
*/
&.is-button-pressed {
box-shadow: inset 0 1px 2px rgba(0, 0, 0, 0.2); /* 1 */
}
}
/**
* 1. Center icon and text vertically.
*/
.kbButton__icon,
.kbButton__text {
display: inline-block; /* 1 */
vertical-align: middle; /* 1 */
}
.kbButton__icon {
color: gray;
opacity: 0.5;
}
.kbButton__text {
color: black;
}
.kbButton--primary {
border-color: blue;
// Introduce specificity to color the descendant component.
.kbButton__icon,
.kbButton__text {
color: blue;
}
}
```
```html
<button class="kbButton kbButton--primary">
<div class="kbButton__icon">Submit</div>
<div class="kbButton__text">Submit</div>
</button>
```
## Rules
### Use uniquely-named "base classes" to represent components
This component will be represented in the styles as a **base class**:
```less
// We can use a namespace like "kb" to make sure we don't affect
// other styles accidentally, especially when we're using a generic
// name like "button".
.kbButton {
background-color: gray;
color: black;
border-radius: 4px;
padding: 4px;
}
```
### Create "descendant classes" to represent child components which can't stand on their own
In this example, the text and the icon are very tightly coupled to the button
component. They aren't supposed to be used outside of this component. So we
can indicate this parent-child relationship with a double-underscore and by
indenting the **descendant classes**.
```less
.kbButton {
/* ... */
}
.kbButton__icon {
display: inline-block;
vertical-align: middle;
}
.kbButton__text {
display: inline-block;
vertical-align: middle;
font-weight: 300;
}
```
```html
<button class="kbButton">
<div class="kbButton__icon fa fa-trophy"></div>
<div class="kbButton__text">Winner</div>
</button>
```
### Think of deeply-nested child components as "subcomponents" instead of descendants
Some components can have subcomponents that have their own subcomponents, and so on.
In this kind of situation, using the descendant class rule above, would get
pretty hairy. Consider a table component:
```less
// ======================== Bad! ========================
// These styles are complex and the multiple double-underscores increases noise
// without providing much useful information.
.kbTable {
/* ... */
}
.kbTable__body {
/* ... */
}
.kbTable__body__row {
/* ... */
}
.kbTable__body__row__cell {
/* ... */
}
```
In this situation, it's better to create separate subcomponent base classes
in their own files. It's important to still name the classes in a way that
indicates their relationship, by incorporating the name of the root base class.
```less
// kbTable.less
.kbTable {
/* ... */
}
```
```less
// kbTableBody.less
.kbTableBody {
/* ... */
}
```
```less
// kbTableRow.less
.kbTableRow {
/* ... */
}
.kbTableRow__cell {
/* ... */
}
```
This is an example of how we can use files and class names to scale a component
as it grows in complexity.
### Represent states with "state classes"
If a user interacts with a component, or a change in application state needs to
be surfaced in the UI, then create **state classes**. These classes will be applied
to components in response to these changes.
Notice that all states begin with a boolean keyword, typically "is-".
```less
.kbButton {
/* ... */
/**
* 1. This button can appear in a "pressed" aka "pinned" state.
*/
&.is-button-pressed {
box-shadow: inset 0 1px 2px rgba(0, 0, 0, 0.2); /* 1 */
}
}
```
### Variations on a component are represented with "modifier classes"
If the UI calls for a component to change along a single axis of semantic
meaning, create modifier classes. **Modifier classes** are different than states,
in that they will not be applied to a component as a result of user interaction
or a change in application state.
```less
.kbButton {
/* ... */
}
.kbButton--primary {
color: white;
background-color: blue;
}
.kbButton--danger {
color: white;
background-color: red;
}
```
```html
<button class="kbButton kbButton--danger">
Delete everything
<button>
```
### Don't use multiple modifier classes together
If the design calls for buttons that look like this:
```
+------------+
| |
| Button |
| |
+------------+
+------------+
| |
| BUTTON |
| |
+------------+
```
It might be tempting to create modifiers that can be combined, like this:
```less
// ======================== Bad! ========================
.kbButton--large {
padding: 20px;
}
.kbButton--loud {
text-transform: uppercase;
}
```
```html
<button class="kbButton kbButton--large">
Button
</button>
<button class="kbButton kbButton--large kbButton--loud">
Button
</button>
```
Down this path lies trouble. Each class loses its semantic meaning and essentially
becomes an inline style. So usually trying to use multiple modifier classes
together is a _code smell_.
Instead of this, it's important to **talk with the designer** and assign a semantic
name to each of these types of buttons, which can then be reflected with
unique base or modifier classes. Discussing use cases and defining the role of
the component is a good way to approach this conversation.
```
+---------------------+
| |
| Call-out button |
| |
+---------------------+
+-----------------------------+
| |
| PRIMARY CALL-OUT BUTTON |
| |
+-----------------------------+
```
```less
// This button is used for calls-to-action, e.g. "Sign up for our newsletter".
// Generally, no more than one will ever appear on a given page.
.kbCallOutButton {
background-color: gray;
color: black;
border-radius: 4px;
padding: 20px;
}
.kbCallOutButton--primary {
text-transform: uppercase;
}
```
```html
<button class="kbCallOutButton">
Call-out button
</button>
<button class="kbCallOutButton kbCallOutButton--primary">
Primary call-out button
</button>
```
### How to apply DRY
The above example might look counter-DRY to you, since the kbButton and
kbCallOutButton have so many common properties.
In general, it's more important to keep styles tightly-scoped to clearly-defined
components (which increases readability and maintainabilty) than it is to keep
them DRY.
But if you really think there is a compelling reason to deduplicate code, then
try using a mixin.
```less
// Use the suffix "mixin" to avoid confusing this with a base class.
.kbButtonMixin {
background-color: gray;
color: black;
border-radius: 4px;
}
.kbButton {
&:extend(.kbButtonMixin all);
}
.kbCallOutButton {
&:extend(.kbButtonMixin all);
}
```
#### Compelling reasons for using mixins
A super-compelling reason to use mixins is if you see that a set of different
components have a set of the same rules applied to all of them, and that it's
likely that any change made to one of them will have to made to the rest, too
(it might be a good idea to double-check this with the designer).
In this case, a mixin can be very useful because then you only need to make the
change in one place. Consider the above `kbButtonMixin` example. Now if the
border-radius changes for all buttons, you only need to change it there. Or if
the designers anticipate that all new types of buttons should have the same
border-radius, then you can just extend this mixin when you create a new button
base class.

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# Html Style Guide
## Multiple attribute values
When a node has multiple attributes that would cause it to exceed the line character limit, each attribute including the first should be on its own line with a single indent. Also, when a node that is styled in this way has child nodes, there should be a blank line between the opening parent tag and the first child tag.
```
<ul
attribute1="value1"
attribute2="value2"
attribute3="value3">
<li></li>
<li></li>
...
</ul>
```

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# JavaScript Style Guide
## Attribution
This JavaScript guide forked from the [node style guide](https://github.com/felixge/node-style-guide) created by [Felix Geisendörfer](http://felixge.de/) and is
licensed under the [CC BY-SA 3.0](http://creativecommons.org/licenses/by-sa/3.0/)
license.
## 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.
## 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][hnsemicolons], 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.
[the opposition]: http://blog.izs.me/post/2353458699/an-open-letter-to-javascript-leaders-regarding
[hnsemicolons]: http://news.ycombinator.com/item?id=1547647
## 120 characters per line
Try to limit your lines to 80 characters. If it feels right, you can go up to 120 characters.
## Use single quotes
Use single quotes, unless you are writing JSON.
*Right:*
```js
var foo = 'bar';
```
*Wrong:*
```js
var foo = "bar";
```
## Opening braces go on the same line
Your opening braces go on the same line as the statement.
*Right:*
```js
if (true) {
console.log('winning');
}
```
*Wrong:*
```js
if (true)
{
console.log('losing');
}
```
Also, notice the use of whitespace before and after the condition statement.
## Always use braces for multi-line code
*Right:*
```js
if (err) {
return cb(err);
}
```
*Wrong:*
```js
if (err)
return cb(err);
```
## Prefer multi-line conditionals
But single-line conditionals are allowed for short lines
*Preferred:*
```js
if (err) {
return cb(err);
}
```
*Allowed:*
```js
if (err) return cb(err);
```
## Declare one variable per var statement
Declare one variable per var statement, it makes it easier to re-order the
lines. However, ignore [Crockford][crockfordconvention] when it comes to
declaring variables deeper inside a function, just put the declarations wherever
they make sense.
*Right:*
```js
var keys = ['foo', 'bar'];
var values = [23, 42];
var object = {};
while (keys.length) {
var key = keys.pop();
object[key] = values.pop();
}
```
*Wrong:*
```js
var keys = ['foo', 'bar'],
values = [23, 42],
object = {},
key;
while (keys.length) {
key = keys.pop();
object[key] = values.pop();
}
```
[crockfordconvention]: http://javascript.crockford.com/code.html
## 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:*
```js
var adminUser = db.query('SELECT * FROM users ...');
```
*Wrong:*
```js
var admin_user = db.query('SELECT * FROM users ...');
```
## Use UpperCamelCase for class names
Class names should be capitalized using `UpperCamelCase`.
*Right:*
```js
function BankAccount() {
}
```
*Wrong:*
```js
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][const] extension, but
unfortunately that cannot be applied to class members, nor is it part of any
ECMA standard.
*Right:*
```js
var SECOND = 1 * 1000;
function File() {
}
File.FULL_PERMISSIONS = 0777;
```
*Wrong:*
```js
const SECOND = 1 * 1000;
function File() {
}
File.fullPermissions = 0777;
```
[const]: https://developer.mozilla.org/en/JavaScript/Reference/Statements/const
## Magic numbers
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:*
```js
var minWidth = 300;
if (width < minWidth) {
...
}
```
*Wrong:*
```js
if (width < 300) {
...
}
```
## Global definitions
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.
## Function definitions
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:*
```js
function myFunc() {
...
}
```
*Allowed:*
```js
var myFunc = function () {
...
};
```
## Object / Array creation
Use trailing commas and put *short* declarations on a single line. Only quote
keys when your interpreter complains:
*Right:*
```js
var a = ['hello', 'world'];
var b = {
good: 'code',
'is generally': 'pretty'
};
```
*Wrong:*
```js
var a = [
'hello', 'world'
];
var b = {"good": 'code'
, is generally: 'pretty'
};
```
## Object / Array iterations, transformations and operations
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:*
```js
var userNames = users.map(function (user) {
return user.name;
});
// examples where lodash makes the code more readable
var userNames = _.pluck(users, 'name');
```
*Wrong:*
```js
var userNames = [];
for (var i = 0; i < users.length; i++) {
userNames.push(users[i].name);
}
```
## Use the === operator
Programming is not about remembering [stupid rules][comparisonoperators]. Use
the triple equality operator as it will work just as expected.
*Right:*
```js
var a = 0;
if (a !== '') {
console.log('winning');
}
```
*Wrong:*
```js
var a = 0;
if (a == '') {
console.log('losing');
}
```
[comparisonoperators]: https://developer.mozilla.org/en/JavaScript/Reference/Operators/Comparison_Operators
## Only use ternary operators for small, simple code
And **never** use multiple ternaries together
*Right:*
```js
var foo = (a === b) ? 1 : 2;
```
*Wrong:*
```js
var foo = (a === b) ? 1 : (a === c) ? 2 : 3;
```
## Do not extend built-in prototypes
Do not extend the prototype of native JavaScript objects. Your future self will
be forever grateful.
*Right:*
```js
var a = [];
if (!a.length) {
console.log('winning');
}
```
*Wrong:*
```js
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 variables, broken into
several names variables, or converted to be a function:
*Right:*
```js
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:*
```js
if (
thing instanceof Shape
&& !(thing instanceof Square)
&& thing.size > 10
) {
console.log('bigger than ten?? Woah!');
}
```
## Name regular expressions
*Right:*
```js
var validPasswordRE = /^(?=.*\d).{4,}$/;
if (password.length >= 4 && validPasswordRE.test(password)) {
console.log('password is valid');
}
```
*Wrong:*
```js
if (password.length >= 4 && /^(?=.*\d).{4,}$/.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:*
```js
function isPercentage(val) {
if (val < 0) return false;
if (val > 100) return false;
return true;
}
```
*Wrong:*
```js
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:
```js
function isPercentage(val) {
var isInRange = (val >= 0 && val <= 100);
return isInRange;
}
```
## Chaining operations
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:*
```js
$('.someClass')
.addClass('another-class')
.append(someElement)
```
```js
d3.selectAll('g.bar')
.enter()
.append('thing')
.data(anything)
.exit()
.each(function() ... )
```
```js
$http.get('/info')
.then(({ data }) => this.transfromInfo(data))
.then((transformed) => $http.post('/new-info', transformed))
.then(({ data }) => console.log(data));
```
*Wrong:*
```js
$('.someClass')
.addClass('another-class')
.append(someElement)
```
```js
d3.selectAll('g.bar')
.enter().append('thing').data(anything).exit()
.each(function() ... )
```
```js
$http.get('/info')
.then(({ data }) => this.transfromInfo(data))
.then((transformed) => $http.post('/new-info', transformed))
.then(({ data }) => console.log(data));
```
## Name your closures
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:*
```js
req.on('end', function onEnd() {
console.log('winning');
});
```
*Wrong:*
```js
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:*
```js
setTimeout(function() {
client.connect(afterConnect);
}, 1000);
function afterConnect() {
console.log('winning');
}
```
*Wrong:*
```js
setTimeout(function() {
client.connect(function() {
console.log('losing');
});
}, 1000);
```
## Use slashes for comments
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 its arguments (docblock) should start with `/**`, contain a single `*` at the beginning of each line, and end with `*/`.
*Right:*
```js
// '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:*
```js
// 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) {
// ...
}
```
## Do not comment out code
We use a version management system. If a line of code is no longer needed, remove it, don't simply comment it out.
## Classes/Constructors and Inheritance
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.
### Capitalized function definition as Constructors
When Defining a Class/Constructor, use the function definition syntax.
*Right:*
```js
function ClassName() {
}
```
*Wrong:*
```js
var ClassName = function () {};
```
### Inheritance should be done with a utility
While you can do it with pure JS, a utility will remove a lot of boilerplate, and be more readable and functional.
*Right:*
```js
// 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:*
```js
function Square(width, height) {
this.width = width;
this.height = height;
}
Square.prototype = Object.create(Shape);
```
### Keep Constructors Small
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 its Super class). This is all that should be done within constructors.
Try to follow the [Write small functions](#write-small-functions) rule here too.
### Use the prototype
If a method/property *can* go on the prototype, it probably should.
```js
function Square() {
...
}
/**
* method does stuff
* @return {undefined}
*/
Square.prototype.method = function () {
...
}
```
### Handling scope and aliasing `this`
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:*
```js
Square.prototype.doFancyThings = function () {
var self = this;
somePromiseUtil()
.then(function (result) {
self.prop = result.prop;
});
}
```
*Wrong:*
```js
Square.prototype.doFancyThings = function () {
somePromiseUtil()
.then(function (result) {
this.prop = result.prop;
}).bind(this);
}
```
*Allowed:*
```js
Square.prototype.area = function () {
return this.width * this.height;
}
```
## Object.freeze, Object.preventExtensions, Object.seal, with, eval
Crazy shit that you will probably never need. Stay away from it.
## Getters and Setters
Feel free to use getters that are free from [side effects][sideeffect], 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.
[sideeffect]: http://en.wikipedia.org/wiki/Side_effect_(computer_science)