eslint-plugin-chai-expect

4.1.0 verified Sat Apr 25 auth: no javascript

An ESLint plugin that checks for common chai.js expect() mistakes. Current stable version is 4.1.0, released April 2026. Supports ESLint 2.x to 10.x and Node.js 20+. Key differentiators: includes auto-fix for some rules, provides both legacy and flat config presets, and has configurable rules for custom chai extensions. Default recommended rules cover missing assertions, inner comparisons/literals, terminating properties used as functions, and uncalled assertion methods.

Common errors

error Error [ERR_REQUIRE_ESM]: require() of ES Module /path/to/node_modules/eslint-plugin-chai-expect/index.js from /path/to/file.js not supported. ↓

cause Using CommonJS require() to load the ESM-only plugin in v4+.

fix

Use import syntax or dynamic import(). Also ensure your project is configured as ESM (type: 'module' in package.json) or use a compatible import() call.

error Configuration for rule "chai-expect/missing-assertion" is invalid: Value "2" is invalid. ↓

cause Using numeric severity (2) in flat config; flat config expects string severity ("error" or "warn").

fix

Use "error" instead of 2, e.g., { "chai-expect/missing-assertion": "error" }.

error ESLint couldn't find the plugin "chai-expect". ↓

cause Plugin not installed or missing in plugins section; for flat config, you must import and add to plugins object.

fix

Run npm install --save-dev eslint-plugin-chai-expect, then add the plugin to plugins in config (import chaiExpectPlugin from 'eslint-plugin-chai-expect'; { plugins: { 'chai-expect': chaiExpectPlugin } }).

Warnings

breaking Dropped support for Node.js < 20 in v4.0.0 ↓

fix Upgrade Node.js to version 20 or higher.

breaking Package is ESM-only since v4; no CommonJS require() for default import ↓

fix Use import syntax (e.g., import chaiExpectPlugin from 'eslint-plugin-chai-expect') or switch to dynamic import().

deprecated recommended config is legacy; use recommended-flat for flat config ↓

fix Use chaiExpectPlugin.configs['recommended-flat'] in eslint.config.js instead of .eslintrc.

gotcha The terminating-properties rule may false-positive on non-terminal chaining if custom properties are not configured ↓

fix If using chai extensions like chai-http, add their terminating properties to the rule options: { properties: ['headers', 'html', 'ip', 'json', 'redirect', 'text'] }.

Install

npm install eslint-plugin-chai-expect

yarn add eslint-plugin-chai-expect

pnpm add eslint-plugin-chai-expect

Imports

plugin (default)
wrong
```
const chaiExpectPlugin = require('eslint-plugin-chai-expect')
```
correct
```
import chaiExpectPlugin from 'eslint-plugin-chai-expect'
```
Module is ESM-only since v4. CommonJS require() is not supported for the default export. For flat config, import as default.

rules

wrong

const { rules } = require('eslint-plugin-chai-expect')

correct

import { rules } from 'eslint-plugin-chai-expect'

Named export for rules. Also ESM-only since v4.

configs['recommended']
```
chaiExpectPlugin.configs.recommended
```
Legacy config preset for .eslintrc. Not available as a direct named import; access via plugin object.
configs['recommended-flat']
```
chaiExpectPlugin.configs['recommended-flat']
```
Flat config preset for eslint.config.js. Available in v4+. Access via plugin object.

Quickstart

Shows how to set up the plugin with both flat and legacy config, including recommended presets and custom rules.

// Install: npm install --save-dev eslint-plugin-chai-expect

// eslint.config.js (flat config, ESLint >=9)
import chaiExpectPlugin from 'eslint-plugin-chai-expect';

export default [
  chaiExpectPlugin.configs['recommended-flat'],
  {
    rules: {
      'chai-expect/no-inner-compare': 'error',
      'chai-expect/missing-assertion': 'error'
    }
  }
];

// .eslintrc.json (legacy config, ESLint <9)
// {
//   "plugins": ["chai-expect"],
//   "extends": ["plugin:chai-expect/recommended"],
//   "rules": {
//     "chai-expect/no-inner-compare": 2
//   }
// }