https://github.com/purely-functional/eslint-plugin-pure

https://github.com/purely-functional/eslint-plugin-pure

Last synced: about 2 months ago
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• Host: GitHub
• URL: https://github.com/purely-functional/eslint-plugin-pure
• Owner: purely-functional
• Created: 2016-05-29T01:54:09.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2016-06-07T15:41:40.000Z (over 8 years ago)
• Last Synced: 2024-04-22T12:30:39.849Z (5 months ago)
• Language: JavaScript
• Size: 8.79 KB
• Stars: 28
• Watchers: 2
• Forks: 1
• Open Issues: 1
• Metadata Files:
  • Readme: README.md

Awesome Lists containing this project

• awesome-eslint - pure - Enforce pure functions (without side effects). (Plugins / Practices and Specific ES Features)

README

        
# eslint-plugin-pure

Enforce rules to make your code purely functional by disallowing some language constructs.

__Note:__ Your code must be using ES6 modules, because `module.exports =` is considered impure code!

## What are disallowed?

- __ExpressionStatements__ are disallowed. ExpressionStatements are statements whose result is not used (i.e. not stored in a variable, thrown, or returned). This signifys that some side-effect is taking place.

  ```js

  array.push(1)

  ```

  Binding to a variable is allowed, though, e.g.

  

  ```js

  export function getArrayLength (array) {

    const arrayLength = array.length

    return arrayLength

  }

  ```

  To prevent cheating by just binding side-effect to an unused variable, use `no-unused-vars` rule.

- __AssignmentExpressions__ are disallowed for obvious reasons.

- __UpdateExpressions__ are disallowed for obvious reasons.

- __SequenceExpressions__ are disallowed, because `(a, b, c)` results in `c`, and that means `a` and `b` are evaluated for purely side-effects.

## Installation

You'll first need to install [ESLint](http://eslint.org):

```

$ npm i eslint --save-dev

```

Next, install `eslint-plugin-pure`:

```

$ npm install purely-functional/eslint-plugin-pure --save-dev

```

**Note:** If you installed ESLint globally (using the `-g` flag) then you must also install `eslint-plugin-pure` globally.

## Usage

Add `pure` to the plugins section of your `.eslintrc` configuration file. You can omit the `eslint-plugin-` prefix:

```yaml

plugins:

  - pure

```

Then in the files you want to make pure, put this comment in:

```js

/* eslint pure/pure: 2 */

```

Use these built-in recommended rules. These rules are useful outside of pure code but when used in conjunction with this plugin yields a powerful effect:

```yaml

rules:

  no-var: 2

  prefer-const: 2

  no-undef: 2

  no-unused-vars: 2

```

Also look into [eslint-plugin-immutable](https://github.com/jhusain/eslint-plugin-immutable) for even more enforcement (such as disallowing `this`).

## Should I use this everywhere?

Probably not.

I recommend using this in your reducers or in entity modules.

## Supported Rules

* [pure](docs/rules/pure.md)