var phone = '13312341234'; function substrPhone(phone, replace, num1, num2) { var start = phone.substring(0, num1); var end = phone.substring(phone.length - num2, phone.length); console.log(end); return start + replace + end; } var newPhone = substrPhone(phone, '********', 3, 0); console.log(newPhone) // 133********