javascript - Reuse capturing group pattern in JS regex

Question

I want to test whether a string is 8 digits or the same number can be divided into 4 parts separated by a -.

I have a regex that does work:

/^d{2}([-]?)(d{2})1d{2}1d{2}$/

And I can prove:

/^d{2}([-]?)(d{2})1d{2}1d{2}$/.test('12345678'); // true
/^d{2}([-]?)(d{2})1d{2}1d{2}$/.test('12-34-56-78');  // true
/^d{2}([-]?)(d{2})1d{2}1d{2}$/.test('12-45-7810'); // false
/^d{2}([-]?)(d{2})1d{2}1d{2}$/.text('-12-45-78-10'); //false

I would have liked to have created a group from d{2} but I tried this:

/^(d{2})([-]?)12121$/

But it does not match anything.

Answer 1

You can write even shorter: ^dd(-dd){3}$|^d{8}$