ServiceNow - GlideDateTime Formatting 

See with examples how to parse and format date and time using GlideDateTime leveraging the SimpleDataFormat patters.
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Code Examples:
gs.info(" --- Example 1 ---");
var gdt = new GlideDateTime("2013-04-02 14:00:00");
// using current user session timezone (Central Time)
gdt.setDisplayValue("21-5-1983 20:00:00", "dd-MM-yyyy HH:mm:ss");
gs.info(gdt.getValue());
gs.info(" --- Example 2 ---");
var gDate = new GlideDate();
gs.info(gDate.getByFormat('yyyy-MM-dd HH:mm:ss'));
gs.info(gDate.getByFormat('MMMM dd, yyyy HH:mm:ss'));
gs.info(" --- Example 3 ---");
gdt = new GlideDateTime();
var gd = new GlideDate();
// use Local Time
gd.setValue(gdt.localTime);
gs.info(gd.getByFormat("yyyy-MM-dd HH:mm:ss"));
gs.info(" --- Example 4 ---");
gdt.setDisplayValue('20151003 23:30:45','yyyyMMdd HH:mm:ss');
gs.info(gdt.getDisplayValue());
gs.info(" --- Example 5 ---");
gdt = new GlideDateTime();
// E = Day name in week
// K = Hour in am/pm (0-11)
gdt.setDisplayValue('Friday, August 18, 2017 8:00 AM', "E, MMM dd, yyyy K:mm a");
gs.info(gdt.getDisplayValue());
gs.info(" --- Example 6 ---");
gDate = new GlideDateTime().getDate();
gs.print(gDate.getByFormat('EEE dd MMM'));
gs.print(gDate.getByFormat('EEEE dd MMMM'));
gs.info(" --- Example 7 ---");
(function isWeekday() {
var isWeekday;
var isWeekend;
// Uses your Timezone!
var gDate = new GlideDate();
// returns name of day in Java Object
var day = gDate.getByFormat('EEEE') + "";
switch(day) {
case "Saturday":
case "Sunday":
isWeekday = false;
isWeekend = true;
break;
default:
isWeekday = true;
isWeekend = false;
}
gs.info("isWeekday: " + isWeekday + ", it's " + day);
gs.info("isWeekend: " + isWeekend + ", it's " + day);
})();