no-subtraction-comparison.md

no-subtraction-comparison

📝 Prefer comparing values directly over subtracting and comparing to 0.

💼 This rule is enabled in the following configs: ✅ recommended, ☑️ unopinionated.

🔧💡 This rule is automatically fixable by the --fix CLI option and manually fixable by editor suggestions.

Subtracting two values only to compare the difference with 0 obscures the intent. Comparing the values directly is shorter and clearer.

This pattern is often a leftover from code that previously used a comparator function (for example, (a, b) => a - b).

Examples

// ❌
if (a - b > 0) {}

// ✅
if (a > b) {}

// ❌
if (a - b <= 0) {}

// ✅
if (a <= b) {}

// ❌
if (0 < a - b) {}

// ✅
if (a > b) {}

// ❌
if (a - b === 0) {}

// ✅
if (a === b) {}

Caveats

The rewrite is only behavior-preserving for numbers. For example, "10" - "5" > 0 is true, but "10" > "5" is false, since strings compare lexicographically. The rule auto-fixes strict ordering comparisons (> and <) when both operands are known to be numbers. For non-strict ordering and equality comparisons, it auto-fixes only when both operands are statically known finite numbers. Otherwise, the rule offers a suggestion instead of an auto-fix.

The extra restriction for non-strict ordering and equality comparisons avoids the infinity edge case: Infinity - Infinity is NaN, so Infinity - Infinity >= 0 is false while Infinity >= Infinity is true.