How do I format a Javascript Date?

Question

How do I format this date so that the alert displays the date in MM/dd/yyyy format?

Answer 1

You prototype a method so you never have to do this irritating task again:

Date.prototype.toFormattedString = function (f)
{
    var nm = this.getMonthName();
    var nd = this.getDayName();
    f = f.replace(/yyyy/g, this.getFullYear());
    f = f.replace(/yy/g, String(this.getFullYear()).substr(2,2));
    f = f.replace(/MMM/g, nm.substr(0,3).toUpperCase());
    f = f.replace(/Mmm/g, nm.substr(0,3));
    f = f.replace(/MM\*/g, nm.toUpperCase());
    f = f.replace(/Mm\*/g, nm);
    f = f.replace(/mm/g, String(this.getMonth()+1).padLeft('0',2));
    f = f.replace(/DDD/g, nd.substr(0,3).toUpperCase());
    f = f.replace(/Ddd/g, nd.substr(0,3));
    f = f.replace(/DD\*/g, nd.toUpperCase());
    f = f.replace(/Dd\*/g, nd);
    f = f.replace(/dd/g, String(this.getDate()).padLeft('0',2));
    f = f.replace(/d\*/g, this.getDate());
    return f;
};

(and yes you could chain those replaces, but it's not here for readability before anyone asks)

---

As requested, additional prototypes to support the above snippet.

Date.prototype.getMonthName = function ()
{
    return this.toLocaleString().replace(/[^a-z]/gi,'');
};

//n.b. this is sooo not i18n safe :)
Date.prototype.getDayName = function ()
{
    switch(this.getDay())
    {
        case 0: return 'Sunday';
        case 1: return 'Monday';
        case 2: return 'Tuesday';
        case 3: return 'Wednesday';
        case 4: return 'Thursday';
        case 5: return 'Friday';
        case 6: return 'Saturday';
    }
};

String.prototype.padLeft = function (value, size) 
{
    var x = this;
    while (x.length < size) {x = value + x;}
    return x;
};

and usage example:

alert((new Date()).toFormattedString('dd Mmm, yyyy'));