Question

Regular expressions aren’t exactly my strong suit. I got a regex for validating international phone numbers here. The validation bit works for me but I don’t understand how I can take the regex result and use it to format the number. My question is how do I figure out, from the regex, what the groupings are that I can use to display?

var intl1RegexObj = /^((\+)?[1-9]{1,2})?([-\s\.])?((\(\d{1,4}\))|\d{1,4})(([-\s\.])?[0-9]{1,12}){1,2}$/;


if (IntlRegexObj.test(businessPhoneValue)) 
{
    var formattedPhoneNumber = businessPhoneValue.replace(IntlRegexObj, "($1)");

    // display formatted result
}

Answer 1

After simplifying that mess of a regex:

if (subject.match(/^((?:\+)?[1-9]{1,2})?[\-\s.]?((?:\(\d{1,4}\))|\d{1,4})([\-\s.]?\d{1,12}){1,2}$/)) {
    // Successful match
}

There are now only 3 capturing groups.

First one $1 is easy, the country code with an optional +.

Then you have the local area code, basically 1-4 numbers with / without parentheses optionally prefixed by [-\s.]. That’s $2

Finally you have your the actual phone number which can be from 1 to 24 numbers, including optional space or dot or minus sign [-\s.]

More detailed explanation:

"
^              # Assert position at the beginning of the string
(              # Match the regular expression below and capture its match into backreference number 1
   (?:         # Match the regular expression below
      \+       # Match the character “+” literally
   )?          # Between zero and one times, as many times as possible, giving back as needed (greedy)
   [1-9]       # Match a single character in the range between “1” and “9”
      {1,2}    # Between one and 2 times, as many times as possible, giving back as needed (greedy)
)?             # Between zero and one times, as many times as possible, giving back as needed (greedy)
[-\s.]         # Match a single character present in the list below
               # The character “-”
               # A whitespace character (spaces, tabs, line breaks, etc.)
               # The character “.”
   ?           # Between zero and one times, as many times as possible, giving back as needed (greedy)
(              # Match the regular expression below and capture its match into backreference number 2
               # Match either the regular expression below (attempting the next alternative only if this one fails)
      (?:      # Match the regular expression below
         \(    # Match the character “(” literally
         \d    # Match a single digit 0..9
          {1,4}# Between one and 4 times, as many times as possible, giving back as needed (greedy)
         \)    # Match the character “)” literally
      )
   |           # Or match regular expression number 2 below (the entire group fails if this one fails to match)
      \d       # Match a single digit 0..9
         {1,4} # Between one and 4 times, as many times as possible, giving back as needed (greedy)
)
(              # Match the regular expression below and capture its match into backreference number 3
   [-\s.]      # Match a single character present in the list below
               # The character “-”
               # A whitespace character (spaces, tabs, line breaks, etc.)
               # The character “.”
      ?        # Between zero and one times, as many times as possible, giving back as needed (greedy)
   \d          # Match a single digit 0..9
      {1,12}   # Between one and 12 times, as many times as possible, giving back as needed (greedy)
){1,2}         # Between one and 2 times, as many times as possible, giving back as needed (greedy)
$              # Assert position at the end of the string (or before the line break at the end of the string, if any)
"