I have a span that contains text of the form

var spanHtml = "My Tab Content (7)";

The content is guaranteed to end with a string of the form "(#)" where
"#" is a whole number.  My question is, how would I write a regular
expression that would change the value of #, given another number?
For example, given the above variable, if I had

var newNumber = 15;

I would want the variable spanHtml to contain

"My Tab Content (15)".

I make no claims that this is the best possible solution.  My Regular
Expression knowledge is severely limited.

One small change could be, since you know it is always (#):

var _regexp = /\([0-9]+\)/;
alert(str1.replace(_regexp, '(15)');

Again though, I am sure a regexp guru will along momentarily to suggest
an improvement.