regexIgnoreCaseFlags

Reports regex patterns that can be simplified by using the i (ignore case) flag.

✅ This rule is included in the ts logical presets.

When a character class contains both upper and lower case versions of the same letters, the pattern can be simplified by using the i (ignore case) flag. This makes the regex shorter and clearer by eliminating redundant character class entries.

Examples

❌ Incorrect

const pattern = /[aA]/;

const pattern = /[a-zA-Z]/;

const pattern = /[aAbBcC]/;

✅ Correct

const pattern = /[a]/i;

const pattern = /[a-z]/i;

const pattern = /[abc]/i;

// Only lowercase letters - no redundancy
const pattern = /[a-z]/;

// Only uppercase letters - no redundancy
const pattern = /[A-Z]/;

// Already using the i flag
const pattern = /[a-z]/i;

Options

This rule is not configurable.

When Not To Use It

If you need explicit control over case matching in your regex patterns, or if your codebase intentionally avoids the i flag for performance or compatibility reasons, you might prefer to disable this rule. Some legacy JavaScript environments may have inconsistent behavior with the i flag for non-ASCII characters.

Further Reading

• MDN: Regular expressions - Flags
• MDN: Regular expressions - Case-insensitive matching

Equivalents in Other Linters

• ESLint: regexp/use-ignore-case