As stated in the comments, you can remove the GMT part:
var gmt = str.indexOf("GMT");
var newDate = str.substr(0,gmt-1)
then analyze the data:
var d = Date.parse(newDate);
and finally add the GTM part:
var offset_hour = str.substr(gmt+3, 3);
var offset_min = str.substr(gmt+6);
d.addMinutes(60 * offset_hour + offset_min);
, datejs.