// Return true if the passed string looks like a valid US
// phone number.

// The user may fill out the form field any way they choose
// as long as it has the format of a valid US number. The
// following are examples of valid formats for US numbers
// (refer to the tests below for other variants):

// 555-555-5555 (555)555-5555 (555) 555-5555 555 555 5555
// 5555555555 1 555 555 5555
// For this challenge you will be presented with a string
// such as 800-692-7753 or 8oo-six427676;laskdjf. Your job
// is to validate or reject the US phone number based on any
//  combination of the formats provided above. The area code
// is required. If the country code is provided, you must
// confirm that the country code is 1. Return true if the
// string is a valid US phone number; otherwise return false.

function telephoneCheck(str) {
  // Good luck!
  let strreg=/^(1\s?)?(\(\d{3}\)|\d{3})[\s\-]?\d{3}[\s\-]?\d{4}$/g;
  return !!str.match(strreg);
}

telephoneCheck("555-555-5555"); // a boolean.
telephoneCheck("1 555-555-5555"); // true.
telephoneCheck("1 (555) 555-5555"); // true.
telephoneCheck("5555555555"); // true.
telephoneCheck("555-555-5555"); // true.
telephoneCheck("(555)555-5555"); // true.
telephoneCheck("1(555)555-5555"); // true.
telephoneCheck("555-5555"); // false.
telephoneCheck("5555555"); // false.
telephoneCheck("1 555)555-5555"); // false.
telephoneCheck("1 555 555 5555"); // true.
telephoneCheck("1 456 789 4444"); // true.
telephoneCheck("123**&!!asdf#"); // false.
telephoneCheck("55555555"); // false.
telephoneCheck("(6054756961)"); // false
telephoneCheck("2 (757) 622-7382"); // false.
telephoneCheck("0 (757) 622-7382"); // false.
telephoneCheck("-1 (757) 622-7382"); // false
telephoneCheck("2 757 622-7382"); // false.
telephoneCheck("10 (757) 622-7382"); // false.
telephoneCheck("27576227382"); // false.
telephoneCheck("(275)76227382"); // false.
telephoneCheck("2(757)6227382"); // false.
telephoneCheck("2(757)622-7382"); // false.
telephoneCheck("555)-555-5555"); // false.
telephoneCheck("(555-555-5555"); // false.
telephoneCheck("(555)5(55?)-5555"); // false.