Update

Below you've said:

Sorry, i can't predict date format before, it should be like dd-mm-yyyy or dd/mm/yyyy or dd-mmm-yyyy format finally i wanted to convert all this format to dd-MMM-yyyy format.

That completely changes the question. It'll be much more complex if you can't control the format. There is nothing built into JavaScript that will let you specify a date format. Officially, the only date format supported by JavaScript is a simplified version of ISO-8601: yyyy-mm-dd, although in practice almost all browsers also support yyyy/mm/dd as well. But other than that, you have to write the code yourself or (and this makes much more sense) use a good library. I'd probably use a library like moment.js or DateJS (although DateJS hasn't been maintained in years).

Original answer:

If the format is always dd/mm/yyyy, then this is trivial:

var parts = str.split("/");
var dt = new Date(parseInt(parts[2], 10),
                  parseInt(parts[1], 10) - 1,
                  parseInt(parts[0], 10));

split splits a string on the given delimiter. Then we use parseInt to convert the strings into numbers, and we use the new Date constructor to build a Date from those parts: The third part will be the year, the second part the month, and the first part the day. Date uses zero-based month numbers, and so we have to subtract one from the month number.

Unfortunately I found out that

var mydate = new Date('2014-04-03');
console.log(mydate.toDateString());

returns "Wed Apr 02 2014". I know it sounds crazy, but it happens for some users.

The bulletproof solution is the following:

var parts ='2014-04-03'.split('-');
// Please pay attention to the month (parts[1]); JavaScript counts months from 0:
// January - 0, February - 1, etc.
var mydate = new Date(parts[0], parts[1] - 1, parts[2]); 
console.log(mydate.toDateString());

A better solution, I am now using date.js - https://code.google.com/p/datejs/

I included the script in my html page as this -

<script type="text/javascript" src="path/to/date.js"></script>

Then I simply parsed the date string "2015-01-16 22:15:00" with specifying the format as,

var dateString = "2015-01-16 22:15:00";
var date = Date.parse(dateString, "yyyy-MM-dd HH:mm:ss");

I think this can help you: http://www.mattkruse.com/javascript/date/

There's a getDateFromFormat() function that you can tweak a little to solve your problem.

Update: there's an updated version of the samples available at javascripttoolbox.com