I want to remove part of the string between two special characters (# and ?) including the hash character but NOT including the question mark, so url#hash?param=2 becomes url?param=2

I was able to come up with something like

str.replace( /#.*??/, '?' );

The only problem is when string ends with something like url#hash which leaves me hanging with trailing question mark. How do I exclude question mark itself from replacement?