eslint-plugin-ft-flow

3.0.11 verified Sat Apr 25 auth: no javascript

ESLint plugin providing Flowtype linting rules, maintained by the flow-typed community as a fork of the original eslint-plugin-flowtype. Current version 3.0.11, with regular releases every few months. Unlike the original plugin, it is actively maintained, supports ESLint 9 flat config, and includes additional rules like `no-duplicate-type-union-intersection-members` and `sort-type-union-intersection-members`. Requires `eslint` ^8.56.0 or ^9.0.0 and optionally `hermes-eslint` >=0.15.0.

Common errors

error Error: Plugin 'ft-flow' was conflicted between '.eslintrc.js' and 'eslint.config.js' ↓

cause Mixing legacy and flat configs.

fix

Use only one config format; remove .eslintrc.* if using eslint.config.js.

error TypeError: Cannot destructure property 'getSourceCode' of 'context' as it is undefined. ↓

cause Using an incompatible version of ESLint or outdated plugin version.

fix

Update eslint to ^8.56.0 or ^9.0.0 and eslint-plugin-ft-flow to >=3.0.10.

error Error: Cannot find module 'eslint-plugin-ft-flow' ↓

cause Module not installed or not resolved.

fix

Run npm install eslint-plugin-ft-flow --save-dev

error Parsing error: The keyword 'import' is reserved ↓

cause ESLint is not configured for ES modules.

fix

Set 'sourceType': 'module' in ESLint config or use .mjs extension.

Warnings

breaking Version 3.0.10 deprecated CommonJS require; only ESM imports work. ↓

fix Use import statement instead of require().

deprecated Some rules may be deprecated and replaced; check documentation. ↓

fix Use the recommended rule set and migrate deprecated rules.

gotcha Rule 'define-flow-type' may conflict with ESLint's 'no-unused-vars'. ↓

fix Add 'no-unused-vars': 'off' or configure appropriately.

gotcha Peer dependency hermes-eslint is optional but if used must be >=0.15.0. ↓

fix Install hermes-eslint@^0.15.0 if you need Hermes parsing.

gotcha Flat config (ESLint 9) is supported but not all legacy config formats. ↓

fix Use eslint.config.js flat config; for .eslintrc use version <3.0.0.

Install

npm install eslint-plugin-ft-flow

yarn add eslint-plugin-ft-flow

pnpm add eslint-plugin-ft-flow

Imports

plugin (default)

wrong

const plugin = require('eslint-plugin-ft-flow')

correct

import plugin from 'eslint-plugin-ft-flow'

ESM-only since v3; CommonJS require not supported.

configs

wrong

const configs = require('eslint-plugin-ft-flow').configs

correct

import { configs } from 'eslint-plugin-ft-flow'

Use named import for configs (e.g., recommended).

rules

wrong

const rules = require('eslint-plugin-ft-flow').rules

correct

import { rules } from 'eslint-plugin-ft-flow'

Access rule definitions via named import.

Quickstart

Show how to set up eslint-plugin-ft-flow with ESLint flat config, enabling a few rules for Flowtype linting.

// eslint.config.js (flat config, ESLint 9)
import plugin from 'eslint-plugin-ft-flow';

export default [
  {
    files: ['**/*.js', '**/*.jsx'],
    plugins: {
      'ft-flow': plugin,
    },
    rules: {
      'ft-flow/define-flow-type': 1,
      'ft-flow/use-flow-type': 1,
      'ft-flow/no-weak-types': 2,
    },
  },
];