foreach for javascript, json array

First of all, that parseJSON is unnecessary and actually dangerous. Take it out:

var unavailableDates1 = <?php echo json_encode($noticesDates) ?>;

Then, just use jQuery.map:

var unavailableDates = $.map(unavailableDates1, function(item) {
    return item.RegDate;
});

Using a string like that is dangerous for the following three objects, for example:

• {"key":"Backslash here: \\"}
• {"key":"I'm a horse!"}
• {"key":"Some\\backslash"}

They become, respectively:

• SyntaxError: Unexpected end of input (Single escape escapes end of string)
• SyntaxError: Unexpected identifier (Unescaped single quote breaks out of the string, actually an XSS vulnerability)
• Object
  key: "Someackslash" (\\b becomes the \b backspace control character)
  __proto__: Object

You could escape it again, but there's no need; valid JSON is always a valid JavaScript object, and you can trust your own PHP not to include injection code in there.

var justDates = [];
for (var i=0; i < unavailableDates1.length; i++) {
   justDates.push(unavailableDates1[i]['RegDate']);
}

Each Object ({'RegDate:'date'}) is an item in a javascript array. To get an item you use a numerical index. so to get the first item would be theArray[0] this would give you {"RegDate":"31-03-2011"}. Then to get that particular date string you just have to use the key theArray[0]['RegDate']!. So since you want to go through every member of a list, you should get the list length using .length.

For loops are usually used for this type of iteration and not for..in. because for in can access properties that are undesired! http://javascriptweblog.wordpress.com/2011/01/04/exploring-javascript-for-in-loops/

have a look at how to iterate over an array. You can do something like:

dates = new Array();
unavailableDates1.forEach(function (obj){ 
    dates.push(obj.RegDate);
};

Try the following:

JavaScript:

var x = [{"RegDate":"31-03-2011"},{"RegDate":"29-07-2011"},{"RegDate":"09-08-2011"},{"RegDate":"09-08-2011"},{"RegDate":"09-08-2011"},{"RegDate":"12-08-2011"},{"RegDate":"15-08-2011"},{"RegDate":"15-08-2011"},{"RegDate":"23-08-2011"},{"RegDate":"07-09-2011"},{"RegDate":"09-09-2011"},{"RegDate":"13-10-2011"},{"RegDate":"13-10-2011"},{"RegDate":"13-10-2011"},{"RegDate":"25-10-2011"},{"RegDate":"25-10-2011"},{"RegDate":"03-11-2011"},{"RegDate":"03-11-2011"},{"RegDate":"11-11-2011"},{"RegDate":"16-11-2011"},{"RegDate":"18-11-2011"},{"RegDate":"21-11-2011"},{"RegDate":"02-12-2011"},{"RegDate":"02-12-2011"},{"RegDate":"12-12-2011"}];
var ary = new Array();
for (foo in x) {
    ary.push(x[foo].RegDate);
}
console.log(ary);

jsFiddle example.

I noticed you tag jquery in here as well so, here's a jquery solution:

http://jsfiddle.net/aztechy/DK9KM/

var foo = [
  {"RegDate":"31-03-2011"},
  {"RegDate":"29-07-2011"},
  {"RegDate":"09-08-2011"},
  {"RegDate":"09-08-2011"}
];

var datesArray = [];
$.each(foo, function() {
  datesArray.push(this.RegDate);
});

console.log(datesArray);​

Try This, it may works.

var unavailableDates = [];
for(var i = 0; i < unavailableDates1.length; i++){
    unavailableDates[i] = unavailableDates1[i].RegDate;
}

for(var i=0;i<unavailableDates.length;i++) {
    unavailableDates[i] = unavailableDates[i].RegDate;
}