format date

index.js

Date.prototype.format = function(format) {
    const zeros = ["", "0", "00", "000"];
    const c = {
        "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()
    };
    if (/(y+)/.test(format)) {
        format = format.replace(
            RegExp.$1,
            `${this.getFullYear()}`.substr(4 - RegExp.$1.length)
        );
    }

    for (const k in c) {
        if (new RegExp(`(${k})`).test(format)) {
            format = format.replace(
                RegExp.$1,
                RegExp.$1.length === 1
                    ? c[k]
                    : (zeros[RegExp.$1.length] + c[k]).substr(`${c[k]}`.length)
            );
        }
    }
    return format;
};