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Javascript – How can i make my regex only accept a closing parentheses if it already matched an opening one

I’m trying to make a regex that will only accept phone numbers in the listed formats. However if I end the first three-digit group with a closing parentheses without an opening one at the start, the test will come back true when I want it to return false. What can I do?

1 555-555-5555
1 (555) 555-5555
1(555)555-5555
1 555 555 5555
5555555555
555-555-5555
(555)555-5555

const validNumbers = /^[1]? ?[(]?[0-9]{3}[)]?s?[0-9]{3}[-s]?[0-9]{4}$/i

console.log(validNumbers.test("1 305) 9759003"))
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2

Answers


  1. 0

    In the pattern [(]?[0-9]{3}[)]?, the opening and closing brackets are optional. There is no relationship between those to optional brackets. So, it will match 012, (012, 012) and (012).

    Regex cannot "remember" whether it found a bracket before or not. So, if you only want to match a closing bracket when you got an opening one, you have to explicitly distinguish between the following two patterns:

    • there is an opening bracket, 3 numbers and a closing bracket ([(][0-9]{3}[)]), or
    • there are only 3 numbers ([0-9]{3}).

    This translates to the following regex: ([(][0-9]{3}[)]|[0-9]{3}). The complete regex then looks as follows:

    const validNumbers = /^[1]? ?([(][0-9]{3}[)]|[0-9]{3})s?[0-9]{3}[-s]?[0-9]{4}$/i

    For your test string, we get the following:

    >>> console.log(validNumbers.test("1 305) 9759003"))
false

>>> console.log(validNumbers.test("1 (305) 9759003")) 
true
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  2. 0 
      const validNumbers = /^1? ?(([0-9]{3})|[0-9]{3})[-s]?[0-9]{3}[-s]?[0-9]{4}$/;

    Explaination:

    • ^1? ?: The beginning of the string may include a 1 followed by an optional space.

    • (([0-9]{3})|[0-9]{3}): Matches 3 digits, which may either be enclosed in matching parentheses or stand alone without them.

    • [-s]?: Allows an optional dash (-) or space.

    • [0-9]{3}: Matches the next set of 3 digits.

    • [-s]?: Allows another optional dash or space.

    • [0-9]{4}$: Matches the final set of 4 digits at the end of the string.

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