Javascript conditional regular expression if-then-else

Question

I\'m trying to limit the entries to a specific format.

If the entry has 5500 or 5100 such as 01\\01-5500-000-00 then I want to have this:

^[0-9]{2,}\         


        

Answer 1

Replace this part of the pattern [0-9]{4} with the literal values for 5100/5500:

/^\d{2,}\\\d{2}-(?:5[15]00-\d{3}-|(?!5[15]00)\d{4}-\d{3}-\d{2})$/

• [0-9] is the same thing as \d in JavaScript
• For the else part, use the negative lookahead (?!5[15]00)\d{4} to guarantee it's not 5100/5500.