Regex to check for 4 consecutive numbers

If you want to find any series of 4 digits in a string /\d\d\d\d/ or /\d{4}/ will do. If you want to find a series of exactly 4 digits, use /[^\d]\d{4}[^\d]/. If the string should simply contain 4 consecutive digits use /^\d{4}$/.

Edit: I think you want to find 4 of the same digits, you need a backreference for that. /(\d)\1{3}/ is probably what you're looking for.

Edit 2: /(^|(.)(?!\2))(\d)\3{3}(?!\3)/ will only match strings with exactly 4 of the same consecutive digits.

The first group matches the start of the string or any character. Then there's a negative look-ahead that uses the first group to ensure that the following characters don't match the first character, if any. The third group matches any digit, which is then repeated 3 times with a backreference to group 3. Finally there's a look-ahead that ensures that the following character doesn't match the series of consecutive digits.

This sort of stuff is difficult to do in javascript because you don't have things like forward references and look-behind.

Should the numbers be part of a string, or do you want only the four numbers. In the later case, the regexp should be ^\d{4}$. The ^ marks the beginning of the string, $ the end. That makes sure, that only four numbers are valid, and nothing before or after that.