eslint-plugin-chai-friendly

What is eslint-plugin-chai-friendly?

eslint-plugin-chai-friendly is an ESLint plugin designed to work with the Chai assertion library. It helps developers write cleaner and more maintainable test code by preventing false positives when using Chai's assertion syntax.

What are eslint-plugin-chai-friendly's main functionalities?

No-unused-expressions

This feature allows the use of Chai's 'expect' and 'should' assertions without triggering ESLint's 'no-unused-expressions' rule. It ensures that expressions like 'expect(foo).to.be.true;' are not flagged as errors.

/* eslint chai-friendly/no-unused-expressions: 2 */
expect(foo).to.be.true;

Other packages similar to eslint-plugin-chai-friendly

eslint-plugin-mocha

eslint-plugin-mocha is an ESLint plugin that provides linting rules specific to Mocha test framework. It helps enforce best practices and coding standards in Mocha tests. Unlike eslint-plugin-chai-friendly, which focuses on Chai assertions, eslint-plugin-mocha covers a broader range of Mocha-specific rules.

eslint-plugin-jest

eslint-plugin-jest is an ESLint plugin for Jest testing framework. It includes rules for ensuring best practices and avoiding common pitfalls in Jest tests. While eslint-plugin-chai-friendly is tailored for Chai assertions, eslint-plugin-jest is designed specifically for Jest, providing a different set of rules and utilities.

README

eslint-plugin-chai-friendly

This plugin overrides no-unused-expressions to make it friendly towards chai expect and should statements.

// this
expect(foo).to.be.true;
foo.should.be.true;

// instead of this
expect(foo).to.be.true; // eslint-disable-line no-unused-expressions
foo.should.be.true; // eslint-disable-line no-unused-expressions

Installation

You'll first need to install ESLint:

npm i eslint --save-dev

Next, install eslint-plugin-chai-friendly:

npm install eslint-plugin-chai-friendly --save-dev

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

Usage

Add chai-friendly to the plugins section of your ESLint configuration file. Then disable original no-unused-expressions rule and configure chai-friendly replacement under the rules section.

ESLint 9 flat config format:

import pluginChaiFriendly from 'eslint-plugin-chai-friendly';

export default {
    plugins: {'chai-friendly': pluginChaiFriendly},
    rules: {
        "no-unused-expressions": "off", // disable original rule
        "chai-friendly/no-unused-expressions": "error"
    },
};

Legacy .eslintrc format:

{
    "plugins": [
        "chai-friendly" // you can omit the eslint-plugin- prefix
    ],
    "rules": {
        "no-unused-expressions": 0, // disable original rule
        "chai-friendly/no-unused-expressions": 2
    }
}

If you don't need to tweak the above rule settings, you can instead extend the provided recommended configuration.

ESLint 9 flat config format:

const pluginChaiFriendly = require("eslint-plugin-chai-friendly");

module.exports = [
    pluginChaiFriendly.configs.recommendedFlat,
    // other configurations
]

Legacy .eslintrc format:

{
  "extends": ["plugin:chai-friendly/recommended"]
}

Options

This rule, in its default state, does not require any arguments. If you would like to enable one or more of the following you may pass an object with the options set as follows:

• allowShortCircuit set to true will allow you to use short circuit evaluations in your expressions (Default: false).
• allowTernary set to true will enable you to use ternary operators in your expressions similarly to short circuit evaluations (Default: false).
• allowTaggedTemplates set to true will enable you to use tagged template literals in your expressions (Default: false).
• enforceForJSX set to true will flag unused JSX element expressions (Default: false).

These options allow unused expressions only if all of the code paths either directly change the state (for example, assignment statement) or could have side effects (for example, function call).

More info in the original rule's docs.

Supported Rules

• chai-friendly/no-unused-expressions

TypeScript Compatibility

If you're using TypeScript with @typescript-eslint, you need to disable both the original ESLint rule and the TypeScript ESLint version:

ESLint 9 flat config format:

import pluginChaiFriendly from 'eslint-plugin-chai-friendly';

export default {
    plugins: {'chai-friendly': pluginChaiFriendly},
    rules: {
        "no-unused-expressions": "off", // disable original rule
        "@typescript-eslint/no-unused-expressions": "off", // disable TypeScript ESLint version
        "chai-friendly/no-unused-expressions": "error"
    },
};

Legacy .eslintrc format:

{
    "plugins": [
        "chai-friendly"
    ],
    "rules": {
        "no-unused-expressions": 0, // disable original rule
        "@typescript-eslint/no-unused-expressions": 0, // disable TypeScript ESLint version
        "chai-friendly/no-unused-expressions": 2
    }
}

Note that if you use the recommended configuration, both rules will be disabled automatically.