JS時間フォーマット

/**
 * JS        
 *   ：       ：'yyyy-MM-dd HH:mm:ss'
 *   ： 2017-09-15 10:09:00
 */
Date.prototype.format = function (fmt) {
    var o = {
        "M+": this.getMonth() + 1,
        "d+": this.getDate(),
        "H+": this.getHours(),
        "m+": this.getMinutes(),
        "s+": this.getSeconds(),
        "q+": Math.floor((this.getMonth() + 3) / 3),
        "S": this.getMilliseconds()
    };
    var year = this.getFullYear().toString();
    year = year.length >= 4 ? year : '0000'.substr(0, 4 - year.length) + year;

    if (/(y+)/.test(fmt)) fmt = fmt.replace(RegExp.$1, (year + "").substr(4 - RegExp.$1.length));
    for (var k in o)
        if (new RegExp("(" + k + ")").test(fmt)) fmt = fmt.replace(RegExp.$1, (RegExp.$1.length === 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length)));
    return fmt;
};

var currentTime = new Date().format("yyyy/MM/dd");
console.log(currentTime );