regex to get the number from the end of a string

This regular expression matches numbers at the end of the string.

var matches = str.match(/\d+$/);

It will return an Array with its 0th element the match, if successful. Otherwise, it will return null.

Before accessing the 0 member, ensure the match was made.

if (matches) {
    number = matches[0];
}

jsFiddle.

If you must have it as a Number, you can use a function to convert it, such as parseInt().

number = parseInt(number, 10);