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Rslint

    no-redundant-comparison

    Unreleased

    Configuration

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

export default defineConfig([
  unicornPlugin.configs.recommended,
  {
    rules: {
      'unicorn/no-redundant-comparison': 'error',
    },
  },
]);

    Rule Details

    Disallow comparisons made redundant by an equality check in the same logical AND.

    An equality between references lets the rule compare their conditions, including transitive equalities and stronger numeric bounds. A strict inequality can also make a strict comparison redundant.

    Examples of incorrect code:

    if (a > 0 && b > 0 && a === b) {}
if (a > 0 && b > 2 && a === b) {}
if (a !== 'test' && b !== 'test' && a === b) {}
if (a === 'test' && b !== 'test' && a !== b) {}

    Examples of correct code:

    if (a > 0 && a === b) {}
if (b > 2 && a === b) {}
if (a !== 'test' && a === b) {}
if (a === 'test' && a !== b) {}

    The rule checks && chains. It skips optional chains and chains with explicit side effects between the first and last analyzed comparisons, including calls, tagged templates, assignments and updates. Side effects outside that interval do not prevent the check.

    Fixes and Suggestions

    The rule removes a comparison automatically when preceding conditions already establish it, or it is statically known to be true. The supporting conditions must evaluate without user-defined hooks. Safe removals of ordering comparisons are offered as editor suggestions.

    An edit must also preserve the expression's returned value. In a condition such as if (...) only truthiness matters, but an assigned or returned && expression can produce a string, number or object. A diagnostic has no edit when removing the comparison could change that value or discard a comment.

    Options

    This rule has no options.

    Differences from upstream

    Rslint withholds edits that Unicorn v79.0.0 can offer unsafely:

    • A later condition is not used to justify deleting an earlier guard. Otherwise the edit could expose a previously skipped expression or remove an exception.
    • Property reads, implicit conversions and other evaluations that may invoke user code cannot support an edit. For example, a getter between equality checks could change the variables being compared. Global names without a local binding are also left unchanged because they may be accessor-backed.
    • Removing the final comparison must preserve the returned value. For example, a === b && a === 1 && label && b === 1 is reported without an edit when used as a value: dropping the final comparison could return label instead of true.

    These cases still receive diagnostics for manual review.

    Original Documentation