How can I replace a regex substring match in Javascript?

Question

var str   = \'asd-0.testing\';
var regex = /asd-(\\d)\\.\\w+/;

str.replace(regex, 1);

That replaces the entire string str with

Answer 1

using str.replace(regex, $1);:

var str   = 'asd-0.testing';
var regex = /(asd-)\d(\.\w+)/;

if (str.match(regex)) {
    str = str.replace(regex, "$1" + "1" + "$2");
}

Edit: adaptation regarding the comment