194 lines
6.1 KiB
Markdown
194 lines
6.1 KiB
Markdown
# JavaScript style guide
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We use [Airbnb's JavaScript Style Guide][airbnb-style-guide] and it's accompanying linter to manage most of our JavaScript style guidelines.
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In addition to the style guidelines set by Airbnb, we also have a few specific rules listed below.
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> **Tip:**
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You can run eslint locally by running `yarn eslint`
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## Arrays
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<a name="avoid-foreach"></a><a name="1.1"></a>
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- [1.1](#avoid-foreach) **Avoid ForEach when mutating data** Use `map`, `reduce` or `filter` instead of `forEach` when mutating data. This will minimize mutations in functions ([which is aligned with Airbnb's style guide][airbnb-minimize-mutations])
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```
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// bad
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users.forEach((user, index) => {
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user.id = index;
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});
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// good
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const usersWithId = users.map((user, index) => {
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return Object.assign({}, user, { id: index });
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});
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```
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## Functions
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<a name="limit-params"></a><a name="2.1"></a>
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- [2.1](#limit-params) **Limit number of parameters** If your function or method has more than 3 parameters, use an object as a parameter instead.
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```
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// bad
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function a(p1, p2, p3) {
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// ...
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};
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// good
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function a(p) {
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// ...
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};
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```
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## Classes & constructors
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<a name="avoid-constructor-side-effects"></a><a name="3.1"></a>
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- [3.1](#avoid-constructor-side-effects) **Avoid side effects in constructors** Avoid making some operations in the `constructor`, such as asynchronous calls, API requests and DOM manipulations. Prefer moving them into separate functions. This will make tests easier to write and code easier to maintain.
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```javascript
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// bad
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class myClass {
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constructor(config) {
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this.config = config;
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axios.get(this.config.endpoint)
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}
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}
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// good
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class myClass {
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constructor(config) {
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this.config = config;
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}
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makeRequest() {
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axios.get(this.config.endpoint)
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}
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}
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const instance = new myClass();
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instance.makeRequest();
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```
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<a name="avoid-classes-to-handle-dom-events"></a><a name="3.2"></a>
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- [3.2](#avoid-classes-to-handle-dom-events) **Avoid classes to handle DOM events** If the only purpose of the class is to bind a DOM event and handle the callback, prefer using a function.
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```
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// bad
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class myClass {
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constructor(config) {
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this.config = config;
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}
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init() {
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document.addEventListener('click', () => {});
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}
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}
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// good
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const myFunction = () => {
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document.addEventListener('click', () => {
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// handle callback here
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});
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}
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```
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<a name="element-container"></a><a name="3.3"></a>
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- [3.3](#element-container) **Pass element container to constructor** When your class manipulates the DOM, receive the element container as a parameter.
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This is more maintainable and performant.
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```
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// bad
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class a {
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constructor() {
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document.querySelector('.b');
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}
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}
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// good
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class a {
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constructor(options) {
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options.container.querySelector('.b');
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}
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}
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```
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## Type Casting & Coercion
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<a name="use-parseint"></a><a name="4.1"></a>
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- [4.1](#use-parseint) **Use ParseInt** Use `ParseInt` when converting a numeric string into a number.
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```
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// bad
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Number('10')
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// good
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parseInt('10', 10);
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```
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## CSS Selectors
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<a name="use-js-prefix"></a><a name="5.1"></a>
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- [5.1](#use-js-prefix) **Use js prefix** If a CSS class is only being used in JavaScript as a reference to the element, prefix the class name with `js-`
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```
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// bad
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<button class="add-user"></button>
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// good
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<button class="js-add-user"></button>
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```
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## Modules
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<a name="use-absolute-paths"></a><a name="6.1"></a>
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- [6.1](#use-absolute-paths) **Use absolute paths for nearby modules** Use absolute paths if the module you are importing is less than two levels up.
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```
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// bad
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import GitLabStyleGuide from '~/guides/GitLabStyleGuide';
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// good
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import GitLabStyleGuide from '../GitLabStyleGuide';
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```
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<a name="use-relative-paths"></a><a name="6.2"></a>
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- [6.2](#use-relative-paths) **Use relative paths for distant modules** If the module you are importing is two or more levels up, use a relative path instead of an absolute path.
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```
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// bad
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import GitLabStyleGuide from '../../../guides/GitLabStyleGuide';
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// good
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import GitLabStyleGuide from '~/GitLabStyleGuide';
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```
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<a name="global-namespace"></a><a name="6.3"></a>
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- [6.3](#global-namespace) **Do not add to global namespace**
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<a name="domcontentloaded"></a><a name="6.4"></a>
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- [6.4](#domcontentloaded) **Do not use DOMContentLoaded in non-page modules** Imported modules should act the same each time they are loaded. `DOMContentLoaded` events are only allowed on modules loaded in the `/pages/*` directory because those are loaded dynamically with webpack.
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## Security
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<a name="avoid-xss"></a><a name="7.1"></a>
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- [7.1](#avoid-xss) **Avoid XSS** Do not use `innerHTML`, `append()` or `html()` to set content. It opens up too many vulnerabilities.
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## ESLint
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<a name="disable-eslint-file"></a><a name="8.1"></a>
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- [8.1](#disable-eslint-file) **Disabling ESLint in new files** Do not disable ESLint when creating new files. Existing files may have existing rules disabled due to legacy compatibility reasons but they are in the process of being refactored.
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<a name="disable-eslint-rule"></a><a name="8.2"></a>
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- [8.2](#disable-eslint-rule) **Disabling ESLint rule** Do not disable specific ESLint rules. Due to technical debt, you may disable the following rules only if you are invoking/instantiating existing code modules
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- [no-new][no-new]
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- [class-method-use-this][class-method-use-this]
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> Note: Disable these rules on a per line basis. This makes it easier to refactor in the future. E.g. use `eslint-disable-next-line` or `eslint-disable-line`
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[airbnb-style-guide]: https://github.com/airbnb/javascript
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[airbnb-minimize-mutations]: https://github.com/airbnb/javascript#testing--for-real
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[no-new]: http://eslint.org/docs/rules/no-new
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[class-method-use-this]: http://eslint.org/docs/rules/class-methods-use-this
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