have doubt in validation expression,validation of date as dd/mm/yyyy format

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ASP.NET

recently i have validate date as dd/mm/yyyy format.I search from net and i have some answer as

var datePat = /^(\d{1,2})(\/|-)(\d{1,2})(\/|-)(\d{4})$/;
var matchArray = dateStr.match(datePat); // is the format ok?
if (matchArray == null) {
alert("Please enter date as either mm/dd/yyyy or mm-dd-yyyy.");
return false;
}
month = matchArray[1]; // p@rse date into variables
day = matchArray[3];
year = matchArray[5];
if (month < 1 || month > 12) { // check month range
alert("Month must be between 1 and 12.");
return false;
}
if (day < 1 || day > 31) {
alert("Day must be between 1 and 31.");
return false;
}
if ((month==4 || month==6 || month==9 || month==11) && day==31) {
alert("Month "+month+" doesn`t have 31 days!")
return false;
}
if (month == 2) { // check for february 29th
var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
if (day > 29 || (day==29 && !isleap)) {
alert("February " + year + " doesn`t have " + day + " days!");
return false;
}
}
return true; // date is valid
}

i have understood it but the thing i havent understood is
in line

var datePat = /^(\d{1,2})(\/|-)(\d{1,2})(\/|-)(\d{4})$/;

i have understood the code but the code which i havent understood is that what does line /^(\d{1,2})(\/|-)(\d{1,2})(\/|-)(\d{4})$/ ;
/^ what does it do. and what does $ do? also if i write the above code as (\d{1,2})(\/|-)(\d{1,2})(\/|-)(\d{4}) in javascript will it work.
please help...