JavaScript – How to Get Date in YYYY-MM-DD Format

If you don't want to use a library why not just split the date string and concoct your own date?

var str_date = "1983-24-12",
    arr_date = str_date.split('-'),
    months   = ['', 'January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];

alert(months[arr_date[2]] + ' ' + arr_date[1] + ', ' + arr_date[0]);

Demo: http://jsfiddle.net/9xeBZ/

JavaScript has the Date() object: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date

The problem is that the JavaScript Date() object will not return a string representation of a month. So at some point you will have to create that logic yourself. Also the format you posted ("1983-24-12") is an invalid format for parsing with the Date() object.

function parse(str) {
    if(!/^(\d){8}$/.test(str)) return "invalid date";
    var y = str.substr(0,4),
        m = str.substr(4,2),
        d = str.substr(6,2);
    return new Date(y,m,d);
}

Usage:

parse('20120401');

UPDATE:

As Rocket said, months are 0-based in js...use this if month's aren't 0-based in your string

function parse(str) {
    if(!/^(\d){8}$/.test(str)) return "invalid date";
    var y = str.substr(0,4),
        m = str.substr(4,2) - 1,
        d = str.substr(6,2);
    return new Date(y,m,d);
}

UPDATE:

More rigorous checking for validity of date. Adopted HBP's way to validate date.

function parse(str) {
    var y = str.substr(0,4),
        m = str.substr(4,2) - 1,
        d = str.substr(6,2);
    var D = new Date(y,m,d);
    return (D.getFullYear() == y && D.getMonth() == m && D.getDate() == d) ? D : 'invalid date';
}