Remove all non-numeric characters except one particular one

Question

Forgive me, but regex is simply beyond me. I'm trying to use javascript to remove all non-numeric characters from a user input except the letter "m" in the first position. I had this code which removes all non-numerics:

userInput.replace(/\D/g, '')

I'd like to modify this to not replace an "m" or "M" at the first position in the string, so

m490-333bA

would become

m490333

Any thoughts?

Answer 1

您可以使用类似以下的表达式：

str.replace(/(?!^m)\D/ig, "");

Answer 2

您可以使用负数前瞻 ：

userInput.replace(/(?!^M)\D/gi, '')