带有随机名称的JS变量的Preg_match

I would like to get value from JS variable by PHP function preg_match (because source is external website downloaded by file_get_contents).

How it looks, example:

var dates_012fbb32db259a64dfe333a8538fd6zz = ['2015-08-26','2015-08-27','2015-08-28','2015-08-31','2015-09-01'];

I want get full value of this variable or if possible last element eg. 2015-09-01

What important part "012fbb32db259a64dfe333a8538fd6zz" is random every refresh.

I tried build pattern by myself but not working:

$pattern = '/var dates_^[a-zA-Z0-9]+ = "(.*)";/';       
preg_match($pattern, $source_website, $result);

This will return your last element in offset 1

$pattern = "/var dates_[a-zA-Z0-9]{32} = .*\'([\d]{4}\-[\d]{2}\-[\d]{2})'\];/";    

$result[1] will have the result. NOTE: I have considered the random number to be 32 bit. if not then you can use [a-zA-Z0-9]+ in place of {32}