\d is not validating other numbers

#1

Tell us what’s happening:
i’m wondering why \d is not validating 1 456 789 4444. if \d{4} is limiting whole number to be 4 digit only.
how can i make it so it only also accept whole number.

Your code so far


function telephoneCheck(str) {
  // Good luck!
  let regexp = /^1?(\W*\d{3}\W*)\1\d{4}$/
  return regexp.test(str);
}

telephoneCheck("555-555-5555");
#2

that regex match will valid for a string like
'1 123 123 5555' ( there are two space between the first 123 and the second )

the usage of \1 should be the question

best is to see how the \1 behave on the following example

/// repeating pattern
/^(\d{3})\s(\d{3})$/.test("123 123") // true
/^(\d{3})\s(\d{3})$/.test("123 456") // true

/// repeating result string using back reference
/^(\d{3})\s\1$/.test("123 123") // true
/^(\d{3})\s\1$/.test("123 456") // false, because "456" != "123"

from the above example shows that \1 will use “the result string that has been matched previously” instead of repeating the pattern.

this is probably the problem that you encountered.

#3

thanks @psyperl for help.

#5