How do I extract partial text that changes dynamically?

This case is slightly different from Extracting dynamic text. Here the entire text does not change, but only part of it.

Let us look at a couple of examples. Example 1: An Amount div that shows "Rs 600", where the amount 600 is variable. The text will always contain "Rs" however. We want to extract the amount, i.e. 600. Example 2: A Page indicator div that shows "Page 2 of 5". Here 2 and 5 are variable but the rest of the content is not. We want to extract the current page number, i.e. 2 and the total pages i.e. 5.

Example 1

Consider a div's visible text shows Rs 600. We wish to extract 600 from it.

This is how we can do it. Working code:
var $amount = _getText(_div("/Rs/")); // Assuming that _div("/Rs/") uniquely identifies the div.
var $number = parseInt(_extract($amount, "/Rs (.*)/", true));

Example 2

Another example would be to extract the current page number and total pages from a PageIndicator div that says "Page 2 of 5".

This div can be identified as _div("/Page .* of/").

Working code:
var $str = _getText("_div("/Page .* of/")");
var $pages = _extract($str, "/Page (.*) of (.*)/", true);
var $currentPageNumber = parseInt($pages[0]);
var $numPages = parseInt($pages[1]);