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Style guides and linting

See the relevant style guides for our guidelines and for information on linting:

JavaScript

We defer to Airbnb on most style-related conventions and enforce them with eslint.

See our current .eslintrc for specific rules and patterns.

Common

ESlint

Never disable eslint rules unless you have a good reason. You may see a lot of legacy files with /* eslint-disable some-rule, some-other-rule */ at the top, but legacy files are a special case. Any time you develop a new feature or refactor an existing one, you should abide by the eslint rules.

Never Ever EVER disable eslint globally for a file

// bad
/* eslint-disable */

// better
/* eslint-disable some-rule, some-other-rule */

// best
// nothing :)

If you do need to disable a rule for a single violation, try to do it as locally as possible

// bad
/* eslint-disable no-new */

import Foo from 'foo';

new Foo();

// better
import Foo from 'foo';

// eslint-disable-next-line no-new
new Foo();

When they are needed always place ESlint directive comment blocks on the first line of a script, followed by any global declarations, then a blank newline prior to any imports or code.
```
// bad
/* global Foo */
/* eslint-disable no-new */
import Bar from './bar';

// good
/* eslint-disable no-new */
/* global Foo */

import Bar from './bar';
```
Never disable the no-undef rule. Declare globals with /* global Foo */ instead.

When declaring multiple globals, always use one /* global [name] */ line per variable.

// bad
/* globals Flash, Cookies, jQuery */

// good
/* global Flash */
/* global Cookies */
/* global jQuery */

Modules, Imports, and Exports

Use ES module syntax to import modules

// bad
require('foo');

// good
import Foo from 'foo';

// bad
module.exports = Foo;

// good
export default Foo;

Relative paths

Unless you are writing a test, always reference other scripts using relative paths instead of ~

In app/assets/javascripts:

// bad
import Foo from '~/foo'

// good
import Foo from '../foo';

In spec/javascripts:

// bad
import Foo from '../../app/assets/javascripts/foo'

// good
import Foo from '~/foo';

Avoid using IIFE. Although we have a lot of examples of files which wrap their contents in IIFEs (immediately-invoked function expressions), this is no longer necessary after the transition from Sprockets to webpack. Do not use them anymore and feel free to remove them when refactoring legacy code.

Avoid adding to the global namespace.

// bad
window.MyClass = class { /* ... */ };

// good
export default class MyClass { /* ... */ }

Side effects are forbidden in any script which contains exports

// bad
export default class MyClass { /* ... */ }

document.addEventListener("DOMContentLoaded", function(event) {
  new MyClass();
}

Data Mutation and Pure functions

Strive to write many small pure functions, and minimize where mutations occur.

// bad
const values = {foo: 1};

function impureFunction(items) {
  const bar = 1;

  items.foo = items.a * bar + 2;

  return items.a;
}

const c = impureFunction(values);

// good
var values = {foo: 1};

function pureFunction (foo) {
  var bar = 1;

  foo = foo * bar + 2;

  return foo;
}

var c = pureFunction(values.foo);

Avoid constructors with side-effects

Parse Strings into Numbers

parseInt() is preferable over Number() or +

// bad
+'10' // 10

// good
Number('10') // 10

// better
parseInt('10', 10);

Vue.js

Basic Rules

Only include one Vue.js component per file.

Export components as plain objects:

export default {
  template: `<h1>I'm a component</h1>
}

Naming

Extensions: Use .vue extension for Vue components.

Reference Naming: Use PascalCase for Vue components and camelCase for their instances:

// bad
import cardBoard from 'cardBoard';

// good
import CardBoard from 'cardBoard'

// bad
components: {
  CardBoard: CardBoard
};

// good
components: {
  cardBoard: CardBoard
};

Props Naming:
Avoid using DOM component prop names.

Use kebab-case instead of camelCase to provide props in templates.

// bad
<component class="btn">

// good
<component css-class="btn">

// bad
<component myProp="prop" />

// good
<component my-prop="prop" />


#### Alignment
- Follow these alignment styles for the template method:

  ```javascript
  // bad
  <component v-if="bar"
      param="baz" />

  // good
  <component
    v-if="bar"
    param="baz"
  />

  // if props fit in one line then keep it on the same line
  <component bar="bar" />

Quotes

Always use double quotes " inside templates and single quotes ' for all other JS.

// bad
template: `
  <button :class='style'>Button</button>
`

// good
template: `
  <button :class="style">Button</button>
`

Props

Props should be declared as an object

// bad
props: ['foo']

// good
props: {
  foo: {
    type: String,
    required: false,
    default: 'bar'
  }
}

Required key should always be provided when declaring a prop

// bad
props: {
  foo: {
    type: String,
  }
}

// good
props: {
  foo: {
    type: String,
    required: false,
    default: 'bar'
  }
}

Default key should always be provided if the prop is not required:

// bad
props: {
  foo: {
    type: String,
    required: false,
  }
}

// good
props: {
  foo: {
    type: String,
    required: false,
    default: 'bar'
  }
}

// good
props: {
  foo: {
    type: String,
    required: true
  }
}

Data

data method should always be a function

// bad
data: {
  foo: 'foo'
}

// good
data() {
  return {
    foo: 'foo'
  };
}

Directives

Shorthand @ is preferable over v-on

// bad
<component v-on:click="eventHandler"/>


// good
<component @click="eventHandler"/>

Shorthand : is preferable over v-bind

// bad
<component v-bind:class="btn"/>


// good
<component :class="btn"/>

Closing tags

Prefer self closing component tags

// bad
<component></component>

// good
<component />

Ordering

Order for a Vue Component:
1. name
2. props
3. data
4. components
5. computedProps
6. methods
7. lifecycle methods
8. beforeCreate
9. created
10. beforeMount
11. mounted
12. beforeUpdate
13. updated
14. activated
15. deactivated
16. beforeDestroy
17. destroyed
18. template

SCSS

SCSS

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