consistent-existence-index-check.md

Enforce consistent style for element existence checks with indexOf(), lastIndexOf(), findIndex(), and findLastIndex()

💼 This rule is enabled in the ✅ recommended config.

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

Enforce consistent style for element existence checks with indexOf(), lastIndexOf(), findIndex(), and findLastIndex().

Prefer using index === -1 to check if an element does not exist and index !== -1 to check if an element does exist.

Similar to the explicit-length-check rule.

Examples

const index = foo.indexOf('bar');

// ❌
if (index < 0) {}

// ✅
if (index === -1) {}

const index = foo.indexOf('bar');

// ❌
if (index >= 0) {}

// ✅
if (index !== -1) {}

const index = foo.indexOf('bar');

// ❌
if (index > -1) {}

// ✅
if (index !== -1) {}

const index = foo.lastIndexOf('bar');

// ❌
if (index >= 0) {}

// ✅
if (index !== -1) {}

const index = array.findIndex(element => element > 10);

// ❌
if (index < 0) {}

// ✅
if (index === -1) {}

const index = array.findLastIndex(element => element > 10);

// ❌
if (index < 0) {}

// ✅
if (index === -1) {}