useUnaryMinus (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v2.6.0
Diagnostic Category: lint/nursery/useUnaryMinus
This rule has an unsafe fix.
The default severity of this rule is warning.
Sources:
- Same as unicorn/prefer-unary-minus

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "useUnaryMinus": "error"
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      }
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    }
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  }
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}

Description

Enforce the use of the unary minus operator over multiplying or dividing by -1.

Multiplying or dividing a value by -1 is an indirect way to negate it (flip its sign). The unary minus operator (-x) is shorter and states the intent directly.

The rule reports x * -1, -1 * x, and x / -1. It doesn’t report -1 / x, because dividing -1 by x doesn’t produce -x.

The fix is unsafe because it can change behavior for BigInt values: x * -1 throws a TypeError when x is a BigInt, but -x doesn’t. Biome doesn’t offer a fix when the expression contains comments that the fix would remove.

Examples

Invalid

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const inverted = value * -1;

code-block.js:1:18 lint/nursery/useUnaryMinus  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ Multiplying by -1 is a roundabout way to negate a value.
  
  > 1 │ const inverted = value * -1;
      │                  ^^^^^^^^^^
    2 │ 
  
  ℹ The unary minus operator is shorter and states the intent directly.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use the unary minus operator.
  
    1   │ - const·inverted·=·value·*·-1;
      1 │ + const·inverted·=·-value;
    2 2 │

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const flipped = -1 * someNumber;

code-block.js:1:17 lint/nursery/useUnaryMinus  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ Multiplying by -1 is a roundabout way to negate a value.
  
  > 1 │ const flipped = -1 * someNumber;
      │                 ^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ The unary minus operator is shorter and states the intent directly.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use the unary minus operator.
  
    1 │ const·flipped·=·-1·*·someNumber;
      │                  ----

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const divided = value / -1;

code-block.js:1:17 lint/nursery/useUnaryMinus  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ Dividing by -1 is a roundabout way to negate a value.
  
  > 1 │ const divided = value / -1;
      │                 ^^^^^^^^^^
    2 │ 
  
  ℹ The unary minus operator is shorter and states the intent directly.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use the unary minus operator.
  
    1   │ - const·divided·=·value·/·-1;
      1 │ + const·divided·=·-value;
    2 2 │

Valid

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const inverted = -value;
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const reciprocal = -1 / value;
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const doubled = value * -2;