Convert javascript to date object to mysql date format (YYYY-MM-DD)

Just edit the string instead:

const date = new Date();
const myDate = date.toISOString().replace("T", " ");
const myDateString = myDate.substring(0, myDate.length - 5);

console.log(myDateString);

To get the date:

const date = new Date().toJSON().slice(0, 10)
console.log(date) //2015-07-23

For datetime:

const datetime = new Date().toJSON().slice(0, 19).replace('T', ' ')
console.log(datetime) //2015-07-23 11:26:00

Note that the resulting date/datetime will always be in the UTC timezone.

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.

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.

The shortest version of this answer by Chris Mayhew:

/**
 * MySQL date
 * @param {Date} [date] Optional date object
 * @returns {string}
 */
function mysqlDate(date = new Date()) {
  return date.toISOString().split('T')[0];
}

const date = mysqlDate();
console.log(date);