Javascript date format dd/mm/yy NOT dd/mm/yyyy - do I need to import a library?

To answer part 1 of your question, you current JavaScript probably contains some script similar to this to get the system date: var today = new Date();
and something like this to isolate the year:  var yyyy = today.getFullYear();
To convert the year to 2 digits, change the value returned for the year above into a string and then create a substring of that using the last 2 digits like this: var yyyy = today.getFullYear().toString().substr(-2);

For part 2, I need more info. How are they choosing the date? Do they type in the full date in an entry field or fields? Do they click a date on a calendar? Do they choose a date from a list of available dates? 

Part 1 JS:

//Call the StoryLine player
var player=GetPlayer();

//Get today's date from the computer
var today = new Date();

//Isolate the day, the month and the year from the date
var dd = today.getDate();
var mm = today.getMonth()+1; //January is 0!
var yy = today.getFullYear().toString().substr(-2);

//combine the date elements as mm/dd/yy
//start by creating a leading zero for single digit days and months
if(dd<10) {
dd='0'+dd
}

if(mm<10) {
mm='0'+mm
}

today = mm+'/'+dd+'/'+yy;

//Send to StoryLine variable
player.SetVar("Today's_Date",today);

You sir, are a super star!!

The second part - we are predefining the date - based on when we take the screen recordings - so the user clicks the hotspot on a calendar (but they only have one option ) in a try me scenario - so there isn't any actual date in the system - just what appears visually - does this make sense?? in this particular case it is  24/07/17.... but if I test the course in August for example we wouldn't want the user to book in the past - the year would need to jump forward, I have a current variable based on system date that just shows 2017 called %year% this is what would need to jump to 2018 if the date the user was taking the course had passed 24/07. But it must be based on the system date and jump one year forward - so a user taking the course in August 2018 would see 2019 for example??

Thankyou SOOOOO Much!!!

I am particularly appreciative of you explaining exactly what each line of code is doing!! I am trying to learn more Javascript and become more proficient - and this helps a LOT!!

//Call the StoryLine player
var player=GetPlayer();

//Get today's date from the computer
var today = new Date();

//Isolate the day, the month and the year from the date and convert them to text strings
var dd = today.getDate().toString();
var mm = today.getMonth()+1; //January is 0!
var mm = mm.toString();
var yy = today.getFullYear().toString().substr(-2);

//create a variable that combines the month and day strings
var year = mm+dd

//evaluate the new variable to see if it is past the target date and, if so, convert it to a number and add 1 to it. Note, July 24th is represented here by the number 724. Any dates past this will cause the year to be adjusted +1 from the current year. On January 1st (which will convert to 11) the future current date will be less than the target and the new future year will be used as is (meaning the year for January 1st 2018 will be 2018)
if(year>724) {
year = +yy + +1
} else {
year = +yy
}

//combine the date elements as mm/dd/yy
//start by creating a leading zero for single digit days and months
if(dd<10) {
dd='0'+dd
}
if(mm<10) {
mm='0'+mm
}

today = mm+'/'+dd+'/'+yy;

//Send variables to StoryLine
player.SetVar("Today's_Date",today);
player.SetVar("Year",year);

You can test it by changing this line:
if(year>724) {
to this
if(year>611) {

611 would stand for June 11th so your year variable should change to 18 (for 2018) to make it a future date since today is 6/12/17

Just be sure to change it back to 724 for July 24th after testing.

Brilliant, thank you so much Owen!! - absolute life saver - I'll drop you a line if I have any trouble getting it to work. Very helpful indeed - I love this community!!

 Happy to have helped.

You can also use moment.js which makes things easier.

// set current value in textbox with id CurrentDate, using moment.js
$("#CurrentDate").val( moment().format('MM D, YY') );

Reference 
Thanks

Math is Correct here, you will have to add Moment and jQuery.

But you can also Moment.js without adding jQuery. :)