#prefer-boolean-return

#Configuration

import { defineConfig, unicornPlugin } from '@rslint/core';

export default defineConfig([
  unicornPlugin.configs.recommended,
  {
    rules: {
      'unicorn/prefer-boolean-return': 'error',
    },
  },
]);

#Rule details

Prefer returning a boolean expression directly when an if and its else or the immediately following return return opposite boolean literals.

The rule keeps consecutive guard clauses that return the same value together.

Incorrect code

function isValid(value) {
  if (value > 0) {
    return true;
  }

  return false;
}

function hasItems(items) {
  if (items.length) {
    return true;
  }

  return false;
}

function isInvalid(value) {
  if (value > 0) {
    return false;
  }

  return true;
}

Correct code

function isValid(value) {
  return value > 0;
}

function hasItems(items) {
  return Boolean(items.length);
}

function isInvalid(value) {
  return !(value > 0);
}

#Automatic fixes

The fix returns conditions that already evaluate to booleans directly. It uses Boolean(...) to coerce other positive conditions and ! for inverted conditions. A report has no fix when the edit would discard a comment or when the replacement needs Boolean(...) and a local value shadows the global.

#Options

This rule has no options.

#Differences from upstream

• rslint keeps the diagnostic and withholds a fix that relies on Boolean when the global is disabled in the lint configuration. A TypeScript import type that introduces the name Boolean also prevents inserting a call, since TypeScript can reject the new call.
• Inside a JavaScript with block, the object can provide its own Boolean or Array. rslint only applies fixes that can preserve a boolean return without relying on those built-ins.

An enclosing variable or parameter named Boolean prevents inserting Boolean(...) even when an inner TypeScript type alias has the same name. Calling the parameter in this example could return a string.

function check(value: unknown, Boolean: (value: unknown) => string) {
  {
    type Boolean = string;
    if (value) return true;
    return false;
  }
}

#Original documentation

• Upstream documentation
• Upstream source