no-useless-length-check.md

no-useless-length-check

📝 Disallow useless array length check.

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

🔧 This rule is automatically fixable by the --fix CLI option.

• Array#some() returns false for an empty array. There is no need to check if the array is not empty.
• Array#every() returns true for an empty array. There is no need to check if the array is empty.

We only check .length === 0, .length !== 0, and .length > 0. These zero and non-zero length check styles are allowed in the unicorn/explicit-length-check rule. It is recommended to use them together.

Examples

// ❌
if (array.length === 0 || array.every(Boolean));

// ❌
if (array.length !== 0 && array.some(Boolean));

// ✅
if (array.every(Boolean));

// ❌
if (array.length > 0 && array.some(Boolean));

// ✅
if (array.some(Boolean));

// ❌
const isAllTrulyOrEmpty = array.length === 0 || array.every(Boolean);

// ✅
const isAllTrulyOrEmpty = array.every(Boolean);

// ✅
if (array.length === 0 || anotherCheck() || array.every(Boolean));

// ✅
const isNonEmptyAllTrulyArray = array.length > 0 && array.every(Boolean);

// ✅
const isEmptyArrayOrAllTruly = array.length === 0 || array.some(Boolean);