封装公共函数转换new Date( )为yyyy-mm-dd

function dateToday(datetime) {
    var year = datetime.getFullYear();//获取完整的年份(4位,如:1970)
    var month = datetime.getMonth() + 1;//获取月份(返回0-11,0代表1月,用的时候记得加上1)
    var date = datetime.getDate();//获取日(返回1-31)

    //判断小于等于9月的时候在月份前加一个"0"
    if (month <= 9) {
        month = "0" + month;
    }
    //判断小于等于9号的时候在天数前加一个"0"
    if (date <= 9) {
        date = "0" + date;
    }
    var dateToday;
    dateToday = year + "-" + month + "-" + date;
    return dateToday
}

var a = new Date();
var b = dateToday(a);
console.log(a); // 2021-05-12T02:11:48.939Z
console.log(b); // 2021-05-12