is-true-regex

A robust utility to check if a value is a RegExp object. Works with both JavaScript and TypeScript, supports cross-realm/iframe scenarios, and handles edge cases securely.

Table of Contents

• Features
• Installation
• Usage
  • JavaScript
  • TypeScript
• API
• Security
• Performance
• License

Features

• ✅ TypeScript support with type guards
• ✅ Cross-realm/iframe compatibility
• ✅ Secure against spoofing attempts
• ✅ Handles edge cases and error conditions
• ✅ Zero dependencies
• ✅ High performance with early returns

Installation

npm install is-true-regex

Usage

JavaScript

import isTrueRegex from "is-true-regex";

// Basic usage
isTrueRegex(/abc/); // true
isTrueRegex(new RegExp('abc')); // true
isTrueRegex('abc'); // false
isTrueRegex(null); // false
isTrueRegex(undefined); // false

// Edge cases
isTrueRegex({}); // false
isTrueRegex([]); // false
isTrueRegex(function() {}); // false
isTrueRegex(new Date()); // false

TypeScript

import isTrueRegex from "is-true-regex";

// Type guard usage
const value: unknown = /abc/;
if (isTrueRegex(value)) {
    // value is now typed as RegExp
    value.test('abc'); // TypeScript knows this is safe
}

// Basic usage
isTrueRegex(/abc/); // true
isTrueRegex(new RegExp('abc')); // true
isTrueRegex('abc'); // false

API

isTrueRegex(value: unknown): value is RegExp

Checks if the provided value is a RegExp object. The function is designed to be secure and reliable, handling various edge cases:

• Cross-realm/iframe scenarios
• Objects with manipulated Symbol.toStringTag
• Proxy objects
• Frozen and sealed objects
• Objects with getters that throw
• Objects with circular references
• Subclassed RegExp objects

Parameters

• value (unknown): The value to check

Returns

• boolean: true if the value is a RegExp object, false otherwise

Security

The implementation is designed to be secure against common spoofing attempts:

• Rejects objects that only mimic RegExp properties
• Validates prototype chain integrity
• Handles Symbol.toStringTag manipulation
• Safely handles error conditions

Performance

The implementation is optimized for performance:

• Early returns for null/undefined values
• Early returns for primitive types
• Efficient prototype chain traversal
• No unnecessary property checks

License

MIT