Question

I’m trying to use JavaScript to convert a date object into a valid MySQL date – what is the best way to do this?

Answer 1

Update: Here in 2021, Date.js hasn’t been maintained in years and is not recommended, and Moment.js is in "maintenance only" mode. We have the built-in Intl.DateTimeFormat, Intl.RelativeTimeFormat, and (soon) Temporal instead, probably best to use those. Some useful links are linked from Moment’s page on entering maintenance mode.

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Old Answer:

Probably best to use a library like Date.js (although that hasn’t been maintained in years) or Moment.js.

But to do it manually, you can use Date#getFullYear(), Date#getMonth() (it starts with 0 = January, so you probably want + 1), and Date#getDate() (day of month). Just pad out the month and day to two characters, e.g.:

(function() {
    Date.prototype.toYMD = Date_toYMD;
    function Date_toYMD() {
        var year, month, day;
        year = String(this.getFullYear());
        month = String(this.getMonth() + 1);
        if (month.length == 1) {
            month = "0" + month;
        }
        day = String(this.getDate());
        if (day.length == 1) {
            day = "0" + day;
        }
        return year + "-" + month + "-" + day;
    }
})();

Usage:

var dt = new Date();
var str = dt.toYMD();

Note that the function has a name, which is useful for debugging purposes, but because of the anonymous scoping function there’s no pollution of the global namespace.

That uses local time; for UTC, just use the UTC versions (getUTCFullYear, etc.).

Caveat: I just threw that out, it’s completely untested.