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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][airbnb-js-style-guide] on most style-related
conventions and enforce them with eslint.
See [our current .eslintrc][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
```javascript
// 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
```javascript
// 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.
```javascript
// 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.
```javascript
// bad
/* globals Flash, Cookies, jQuery */
// good
/* global Flash */
/* global Cookies */
/* global jQuery */
```
#### Modules, Imports, and Exports
- Use ES module syntax to import modules
```javascript
// 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**:
```javascript
// bad
import Foo from '~/foo'
// good
import Foo from '../foo';
```
In **spec/javascripts**:
```javascript
// 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.
```javascript
// bad
window.MyClass = class { /* ... */ };
// good
export default class MyClass { /* ... */ }
```
- Side effects are forbidden in any script which contains exports
```javascript
// 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.
```javascript
// 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 `+`
```javascript
// 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:
```javascript
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:
```javascript
// 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.
```javascript
// bad
<component class="btn">
// good
<component cssClass="btn">
```
#### 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.
```javascript
// bad
template: `
<button :class='style'>Button</button>
`
// good
template: `
<button :class="style">Button</button>
`
```
#### Props
- Props should be declared as an object
```javascript
// bad
props: ['foo']
// good
props: {
foo: {
type: String,
required: false,
default: 'bar'
}
}
```
- Required key should always be provided when declaring a prop
```javascript
// 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:
```javascript
// 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
```javascript
// bad
data: {
foo: 'foo'
}
// good
data() {
return {
foo: 'foo'
};
}
```
#### Directives
- Shorthand `@` is preferable over `v-on`
```javascript
// bad
<component v-on:click="eventHandler"/>
// good
<component @click="eventHandler"/>
```
- Shorthand `:` is preferable over `v-bind`
```javascript
// bad
<component v-bind:class="btn"/>
// good
<component :class="btn"/>
```
#### Closing tags
- Prefer self closing component tags
```javascript
// 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
1. `beforeCreate`
2. `created`
3. `beforeMount`
4. `mounted`
5. `beforeUpdate`
6. `updated`
7. `activated`
8. `deactivated`
9. `beforeDestroy`
10. `destroyed`
8. `template`
## SCSS
- [SCSS](style_guide_scss.md)
[airbnb-js-style-guide]: https://github.com/airbnb/javascript
[eslintrc]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/.eslintrc
|