const isValidIPv4 = (ip) => {
    const ipv4Regex = /^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/;
    return ipv4Regex.test(ip);
};

console.log(isValidIPv4("192.168.1.1"));    // true
console.log(isValidIPv4("10.0.0.255"));   // true
console.log(isValidIPv4("0.0.0.0"));     // true
console.log(isValidIPv4("255.255.255.255")); // true
console.log(isValidIPv4("192.168.1.256")); // false (invalid segment)
console.log(isValidIPv4("192.168.1"));    // false (too few segments)
console.log(isValidIPv4("256.0.0.0"));    // false (invalid segment)
console.log(isValidIPv4("192.168.1.1.1")); // false (too many segments)
console.log(isValidIPv4("abc.def.ghi.jkl")); // false (invalid characters)