eslint-plugin-fp

What is eslint-plugin-fp?

eslint-plugin-fp is an ESLint plugin that enforces functional programming best practices. It helps developers write more predictable and maintainable code by avoiding side effects, mutations, and other non-functional programming patterns.

What are eslint-plugin-fp's main functionalities?

No Mutating Methods

This rule disallows the use of mutating array methods like push, pop, shift, unshift, etc., to encourage the use of immutable operations.

/* eslint fp/no-mutating-methods: 'error' */
const arr = [1, 2, 3];
arr.push(4); // This will trigger an ESLint error

No Mutating Assign

This rule prevents the mutation of object properties, promoting the use of immutable data structures.

/* eslint fp/no-mutation: 'error' */
let obj = { a: 1 };
obj.a = 2; // This will trigger an ESLint error

No Let

This rule disallows the use of `let` and `var` to encourage the use of `const` for variable declarations, promoting immutability.

/* eslint fp/no-let: 'error' */
let x = 1; // This will trigger an ESLint error

No This

This rule disallows the use of `this` to avoid issues related to context and state, encouraging the use of pure functions.

/* eslint fp/no-this: 'error' */
class MyClass {
  constructor() {
    this.value = 1; // This will trigger an ESLint error
  }
}

Other packages similar to eslint-plugin-fp

eslint-plugin-immutable

eslint-plugin-immutable enforces immutability rules in JavaScript code. It is similar to eslint-plugin-fp but focuses more on preventing mutations and ensuring data immutability.

eslint-plugin-functional

eslint-plugin-functional is another ESLint plugin that enforces functional programming principles. It provides a broader set of rules compared to eslint-plugin-fp, including rules for immutability, pure functions, and function composition.

eslint-plugin-prefer-let

eslint-plugin-prefer-let enforces the use of `let` over `var` and `const` where appropriate. While it does not focus on functional programming, it helps in writing cleaner and more predictable code by avoiding the pitfalls of `var`.

README

eslint-plugin-fp

ESLint rules for functional programming

Install

$ npm install --save-dev eslint eslint-plugin-fp

Usage

Configure it in package.json.

{
  "name": "my-awesome-project",
  "eslintConfig": {
    "env": {
      "es6": true
    },
    "plugins": [
      "fp"
    ],
    "rules": {
      "fp/no-arguments": "error",
      "fp/no-class": "error",
      "fp/no-delete": "error",
      "fp/no-events": "error",
      "fp/no-get-set": "error",
      "fp/no-let": "error",
      "fp/no-loops": "error",
      "fp/no-mutating-assign": "error",
      "fp/no-mutating-methods": "error",
      "fp/no-mutation": "error",
      "fp/no-nil": "error",
      "fp/no-proxy": "error",
      "fp/no-rest-parameters": "error",
      "fp/no-this": "error",
      "fp/no-throw": "error",
      "fp/no-unused-expression": "error",
      "fp/no-valueof-field": "error",
      "no-var": "error"
    }
  }
}

Rules

• no-arguments - Forbid the use of arguments.
• no-class - Forbid the use of class.
• no-delete - Forbid the use of delete.
• no-events - Forbid the use of the events module.
• no-get-set - Forbid the use of getters and setters.
• no-let - Forbid the use of let.
• no-loops - Forbid the use of loops.
• no-mutating-assign - Forbid the use of Object.assign() with a variable as first argument.
• no-mutating-methods - Forbid the use of mutating methods.
• no-mutation - Forbid the use of mutating operators.
• no-nil - Forbid the use of null and undefined.
• no-proxy - Forbid the use of Proxy.
• no-rest-parameters - Forbid the use of rest parameters.
• no-this - Forbid the use of this.
• no-throw - Forbid the use of throw.
• no-unused-expression - Enforce that an expression gets used.
• no-valueof-field - Forbid the creation of valueOf fields.

Recommended configuration

This plugin exports a recommended configuration that enforces good practices.

To enable this configuration, use the extends property in your package.json.

{
  "name": "my-awesome-project",
  "eslintConfig": {
    "plugins": [
      "fp"
    ],
    "extends": "plugin:fp/recommended"
  }
}

See ESLint documentation for more information about extending configuration files.

MIT © Jeroen Engels

Changelog

[2.3.0] - 2017-01-01

Added

• Added allowUseStrict option to [no-unused-expression] to allow 'use strict'; statements.
• Use [eslint-ast-utils] to replace some logic.

Fixed

• Allow properties named arguments in [no-arguments].
• Allow function expressions in [no-mutating-assign].