Replace capture group of dynamic size

Question

I want to replace the first part of regex for a URL with asterisks. Depending on the regex, for example:

Case 1

http://example.com/pat

Answer 1

You can use the sticky flag y (but Internet Explorer doesn't support it):

s = s.replace(/(^https?:\/\/.*?\/path1\/?|(?!^))./gy, '$1*')

But the simplest (and that is supported everywhere), is to use a function as replacement parameter.

s = s.replace(/^(https?:\/\/.+\/path1\/?)(.*)/, function (_, m1, m2) {
    return m1 + '*'.repeat(m2.length);
});

---

For the second case, you can simply check if there's an @ after the current position:

s = s.replace(/.(?=.*@)/g, '*');