noSubtractionComparison (JavaScript)

Language JavaScript (and super languages)

Caution

This rule is part of the nursery group. This means that it is experimental and the behavior can change at any time.

Summary

• Rule available since: v2.6.6
• Diagnostic Category: lint/nursery/noSubtractionComparison
• This rule has an unsafe fix.
• The default severity of this rule is warning.
• Sources:
  • Same as unicorn/no-subtraction-comparison

How to configure

biome.json

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

Description

Disallow subtracting two values only to compare the result with 0.

Code such as a - b > 0 subtracts one value from another, then checks whether the difference is above, below, or equal to 0. Comparing the two values directly, as in a > b, is shorter and states the intent more clearly.

This pattern often remains after code is copied from a sort comparison function such as (a, b) => a - b.

The rule checks the operators >, >=, <, <=, ===, !==, ==, and !=, with 0 on either side. When 0 is on the left, the fix flips the operator, so 0 < a - b becomes a > b.

Caution

The fix gives the same result only when both values are numbers, so it is unsafe:

• Strings are compared character by character instead of as numbers. "10" - "5" > 0 is true, but "10" > "5" is false.
• === and !== check whether two objects, such as two dates, are the same object. start - end === 0 checks whether two dates hold the same time, but start === end checks whether they are the same date object.
• Infinity - Infinity is NaN (“not a number”), and every comparison with NaN is false. Infinity - Infinity >= 0 is false, but Infinity >= Infinity is true.

Examples

Invalid

if (a - b > 0) {}

code-block.js:1:5 lint/nursery/noSubtractionComparison  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This comparison subtracts two values and compares the difference with 0.
  
  > 1 │ if (a - b > 0) {}
      │     ^^^^^^^^^
    2 │ 
  
  ℹ Compare the two values directly instead, which is shorter and states the intent more clearly.
  
  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: Compare the values directly.
  
    1   │ - if·(a·-·b·>·0)·{}
      1 │ + if·(a·>·b)·{}
    2 2 │   
  

if (a - b <= 0) {}

code-block.js:1:5 lint/nursery/noSubtractionComparison  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This comparison subtracts two values and compares the difference with 0.
  
  > 1 │ if (a - b <= 0) {}
      │     ^^^^^^^^^^
    2 │ 
  
  ℹ Compare the two values directly instead, which is shorter and states the intent more clearly.
  
  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: Compare the values directly.
  
    1   │ - if·(a·-·b·<=·0)·{}
      1 │ + if·(a·<=·b)·{}
    2 2 │   
  

if (0 < a - b) {}

code-block.js:1:5 lint/nursery/noSubtractionComparison  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This comparison subtracts two values and compares the difference with 0.
  
  > 1 │ if (0 < a - b) {}
      │     ^^^^^^^^^
    2 │ 
  
  ℹ Compare the two values directly instead, which is shorter and states the intent more clearly.
  
  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: Compare the values directly.
  
    1   │ - if·(0·<·a·-·b)·{}
      1 │ + if·(a·>·b)·{}
    2 2 │   
  

if (a - b === 0) {}

code-block.js:1:5 lint/nursery/noSubtractionComparison  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This comparison subtracts two values and compares the difference with 0.
  
  > 1 │ if (a - b === 0) {}
      │     ^^^^^^^^^^^
    2 │ 
  
  ℹ Compare the two values directly instead, which is shorter and states the intent more clearly.
  
  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: Compare the values directly.
  
    1   │ - if·(a·-·b·===·0)·{}
      1 │ + if·(a·===·b)·{}
    2 2 │   
  

Valid

if (a > b) {}
if (a - b > 1) {}
if (a + b > 0) {}
if (a - b > 0n) {}

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