Why does this regex make Chrome hang?

Question

Try typing this into Chrome\'s JS console. It\'s a regex I found to check if something\'s a valid URL or not:

\"http://www.kvraudio.com/\".match(/^(https?:\\         


        

Answer 1

Because you have catastrophic backtracking:

([\/\w \.-]*)*

This expression should be modified to remove one of the stars (*):

([\/\w \.-]*)

Note that catastrophic backtracking typically only rears its ugly head when a match cannot be made. That's why the first example you gave executes without any issues.

Your second example exits before it hits the ([...]*)*, so there is no opportunity for the backtracking to take effect.

For a more thorough explanation of catastrophic backtracking, see my answer to this question:
How can I recognize an evil regex?