prefer-math-trunc.md

Enforce the use of Math.trunc instead of bitwise operators

💼 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.

Enforces a convention of using Math.trunc() instead of bitwise operations for clarity and more reliable results. It prevents the use of the following bitwise operations:

• x | 0 (bitwise OR with 0)
• ~~x (two bitwise NOT)
• x >> 0 (Signed Right Shift with 0)
• x << 0 (Left Shift with 0)
• x ^ 0 (bitwise XOR Shift with 0)

These hacks help truncate numbers but they are not clear and do not work in some cases.

This rule is fixable, unless the left-hand side in assignment has side effect.

Examples

const foo = 37.4;

// ❌
console.log(foo | 0);

// ❌
console.log(~~foo);

// ❌
console.log(foo << 0);

// ❌
console.log(foo >> 0);

// ❌
console.log(foo.bar ^ 0);

// ✅
console.log(Math.trunc(foo));

let foo = 37.4;

// ❌
foo |= 0;

// ✅
foo = Math.trunc(foo);

// ✅
const foo = 37.4;
console.log(foo | 3);

// ✅
const foo = 37.4;
console.log(~foo);

// ✅
const foo = 37.4;
console.log(foo >> 3);

// ✅
const foo = 37.4;
console.log(foo << 3);

// ✅
const foo = 37.4;
console.log(foo ^ 3);