@andreasnicolaou/eslint-plugin-conditional-best-practices

Opinionated ESLint rules for cleaner, safer conditionals — limit nesting, prefer early returns, catch duplicate and constant conditions, simplify ternaries, and flag risky eval.

Zero runtime dependencies. Works with ESLint flat config (ESLint 9, and 8.21+) and legacy .eslintrc.

These rules focus on writing clear and efficient conditional statements. They are intentionally opinionated, so feel free to enable only the ones that suit your team.

Installation

npm install -D @andreasnicolaou/eslint-plugin-conditional-best-practices

Usage

Flat config (eslint.config.js) — ESLint 9+ (recommended)

The quickest way is to extend the bundled recommended config, which registers the plugin and turns on every rule at sensible severities:

// eslint.config.js
import conditional from '@andreasnicolaou/eslint-plugin-conditional-best-practices';

export default [conditional.configs.recommended];

Prefer granular control? Register the plugin and pick rules yourself:

// eslint.config.js
import conditional from '@andreasnicolaou/eslint-plugin-conditional-best-practices';

export default [
    {
        plugins: {
            '@andreasnicolaou/conditional-best-practices': conditional,
        },
        rules: {
            '@andreasnicolaou/conditional-best-practices/no-eval': 'error',
            '@andreasnicolaou/conditional-best-practices/no-excessive-nested-conditionals': ['warn', { max: 3 }],
            '@andreasnicolaou/conditional-best-practices/prefer-early-return': 'warn',
        },
    },
];

CommonJS works the same way with require:

const conditional = require('@andreasnicolaou/eslint-plugin-conditional-best-practices');
module.exports = [conditional.configs.recommended];

There is also a conditional.configs.all config that enables every rule as an error.

Legacy config (.eslintrc)

{
    "plugins": ["@andreasnicolaou/conditional-best-practices"],
    "extends": ["plugin:@andreasnicolaou/conditional-best-practices/legacy-recommended"],
}

Rules

✅ = enabled in recommended · 🔧 = autofixable · 💡 = has editor suggestions

| Name | Description | Recommended | Fixable | | :--------------------------------------------------------------------------- | :------------------------------------------------------------------- | :---------: | :-----: | | no-constant-conditionals | Disallow conditionals that always evaluate to true or false. | ✅ | | | no-duplicated-conditions | Disallow duplicate conditions in if/else if chains. | ✅ | | | no-excessive-nested-conditionals | Disallow excessive nesting of conditionals (configurable max). | ✅ | | | no-long-else-if-chains | Limit the number of consecutive else if statements (configurable). | ✅ | | | no-nested-ternary-operators | Disallow nested ternary operators. | ✅ | | | no-useless-ternary | Disallow unnecessary boolean ternaries (x ? true : false). | ✅ | 🔧 | | prefer-early-return | Encourage early returns instead of deeply nested if/else blocks. | ✅ | | | require-default-in-switch | Require a non-empty default case in switch statements. | ✅ | 💡 | | no-eval | Disallow eval() and the Function constructor (security risk). | ✅ | |

Autofixing

Run ESLint with --fix to apply automatic fixes:

npx eslint . --fix

• no-useless-ternary rewrites cond ? true : false → cond and cond ? false : true → !cond.
• require-default-in-switch offers an editor suggestion to insert a default case (suggestions are applied manually from your editor, not by --fix).

The remaining rules report problems without auto-rewriting, since the safe fix depends on intent.

Contributing

Issues and pull requests are welcome at the GitHub repository.

License

MIT © Andreas Nicolaou