eslint-plugin-math

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math/prefer-math-trunc ​

enforce the use of Math.trunc() instead of other truncations

  • ⚙️ This rule is included in "plugin:math/recommended".
  • 🔧 The --fix option on the command line can automatically fix some of the problems reported by this rule.
  • 💡 Some problems reported by this rule are manually fixable by editor suggestions.

📖 Rule Details ​

This rule aims to enforce the use of Math.trunc() instead of other truncation methods for removing the fractional part of numbers.

Math.trunc() provides several advantages over alternative approaches:

  • Clarity of intent: Immediately obvious that you're truncating to an integer
  • Simplicity: Single function call instead of conditional logic
  • Consistency: Standardized approach across all numeric ranges
  • Performance: Optimized native implementation
  • Reliability: Works correctly with all finite numbers, including very large values
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🔧 Options ​

json
{
  "math/prefer-math-trunc": [
    "error",
    {
      "reportBitwise": true // false
    }
  ]
}
  • reportBitwise ... If true, the rule reports bitwise operations that are equivalent to Math.trunc(). Defaults to true.

reportBitwise (boolean) ​

  • Default: true
  • Description: Controls whether the rule reports bitwise operations that can be replaced with Math.trunc()

When true, the rule will flag bitwise operations like:

  • ~~x (double bitwise NOT)
  • x | 0 (bitwise OR with zero)
  • x >> 0 (right shift by zero)
  • x << 0 (left shift by zero)
  • x ^ 0 (bitwise XOR with zero)

When false, the rule only reports conditional expressions and other non-bitwise patterns.

Why Bitwise Operations Are Problematic ​

While bitwise operations can truncate numbers, they have significant limitations:

  • Limited range: Only work correctly for 32-bit signed integers (approximately ±2.1 billion)
  • Unexpected behavior: Large numbers get converted to different values
  • Poor readability: Intent is not immediately clear
  • Platform dependency: Behavior may vary across JavaScript engines
js
// Demonstrating bitwise operation limitations
const largeNumber = 3000000000;

Math.trunc(largeNumber);  // 3000000000 (correct)
~~largeNumber;           // -1294967296 (wrong! 32-bit overflow)
largeNumber | 0;         // -1294967296 (wrong! 32-bit overflow)

📚 Further reading ​

🚀 Version ​

This rule was introduced in eslint-plugin-math v0.1.0

🔍 Implementation ​