Here is a function getlastintstring which would return the last integer string from a string passed
as paramter. 

here is an example 

input:
Hello 100worldthis2000is a test. 

output:
this would return 2000 


function getlastintstring(str) {
    var bnumeric = 0;
    var strlength = str.length;
    var numstr = "";
    for (strlength = strlength; strlength > 0; strlength--) {
        if (IsNumeric(str.substring(strlength, strlength + 1))) {
            numstr = str.substring(strlength, strlength + 1) + numstr;
            bnumeric = 1;
        } else {
            if (bnumeric > 0) {
                return numstr;
            }
        }
    }
    return numstr;
}