What

ESLint rules for functional programming.

NOTE 1 of 2: This is a fork from https://github.com/jfmengels/eslint-plugin-fp. I looked at the 33 forks at the time and none were up to date. So, I forked it, merged in 2 of the outstanding PR's, and added some missing features (allow class constructors, using classes if you extend React.Component, switch statements that have a default with a return value don't violate fp-jxl/no-nil, etc).

NOTE 2 of 2: Beware much of the docs will say things like fp-jxl/no-nil when referring to a rule. Always use that for this library, not fp/no-nil. The fp-jxl is the ESLint plugin suffix, and the no-nil is the rule name. Many places in the documentation and tests refer to fp. Since I don't own the original package, and ESLint is challenging to configure, just assume fp-jxl/some-rule for all rules in the documentation, excluding no-var which is global.

Install

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

Usage

Configure it in package.json.

{
  "name": "my-awesome-project",
  "eslintConfig": {
    "env": {
      "es6": true
    },
    "plugins": [
      "fp-jxl"
    ],
    "rules": {
      "fp-jxl/explicit-return": "off",
      "fp-jxl/must-return": "off",
      "fp-jxl/no-arguments": "error",
      "fp-jxl/no-class": "error",
      "fp-jxl/no-delete": "error",
      "fp-jxl/no-events": "error",
      "fp-jxl/no-exceptions": "off",
      "fp-jxl/no-exports": "off",
      "fp-jxl/no-function-expressions": "off",
      "fp-jxl/no-get-set": "error",
      "fp-jxl/no-ifs": "off",
      "fp-jxl/no-imports": "off",
      "fp-jxl/no-instanceofs": "off",
      "fp-jxl/no-let": "error",
      "fp-jxl/no-loops": "error",
      "fp-jxl/no-mutating-assign": "error",
      "fp-jxl/no-mutating-methods": "error",
      "fp-jxl/no-mutation": "error",
      "fp-jxl/no-new": "off",
      "fp-jxl/no-nil": "error",
      "fp-jxl/no-nulls": "off",
      "fp-jxl/no-proxy": "error",
      "fp-jxl/no-reassigns": "off",
      "fp-jxl/no-rest-parameters": "error",
      "fp-jxl/no-switches": "off",
      "fp-jxl/no-this": "error",
      "fp-jxl/no-throw": "error",
      "fp-jxl/no-typeofs": "off",
      "fp-jxl/no-undefined": "off",
      "fp-jxl/no-unused-expression": "error",
      "fp-jxl/no-valueof-field": "error",
      "fp-jxl/no-variable-declarations": "off",
      "no-var": "error"
    }
  }
}

Rules

• explicit-return - Stricter version of must-return: every function should have a top level return statement.
• must-return - Every branch of every function should have a return statement.
• 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-exceptions - Forbids throwing and catching errors.
• no-exports - Forbids use of export keyword
• no-function-expressions - Forbids the use of function expressions, consider: prefer-arrow-callback
• no-get-set - Forbid the use of getters and setters.
• no-ifs - Forbids the use of if statements, in favour of ternary expressions
• no-imports - Forbids the use of the import keyword, in favour of CommonJS
• no-instanceofs - Forbids the use of the instanceof operator
• 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-new - Forbids the use of the new keyword
• no-nil - Forbid the use of null and undefined.
• no-nulls - Forbids the use of null.
• no-proxy - Forbid the use of Proxy.
• no-reassigns - Forbids reassigning variables
• no-rest-parameters - Forbid the use of rest parameters.
• no-switches - Forbids the use of the switch statement
• no-this - Forbid the use of this.
• no-throw - Forbid the use of throw.
• no-typeofs - Forbids the typeof operator
• no-undefined - Forbids the use of undefined.
• no-unused-expression - Enforce that an expression gets used.
• no-valueof-field - Forbid the creation of valueOf fields.
• no-variable-declarations - Forbids variable declarations, no var or let.

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-jxl/recommended"
  }
}

See ESLint documentation for more information about extending configuration files.

MIT © Jeroen Engels MIT © Ivan Dmitriev MIT © Thomas Grainger MIT © Jesse Warden