The shortest version of https://stackoverflow.com/a/11453710/3777994:
/**
* MySQL date
* @param {Date} [date] Optional date object
* @returns {string}
*/
function mysqlDate(date){
date = date || new Date();
return date.toISOString().split('T')[0];
}
Using:
var date = mysqlDate(); //'2014-12-05'