JS获取日期对应星期几

第一版，方便看懂原理

_getWeek = () => {
var str = "";  
var week = new Date().getDay();  
if (week == 0) {  
        str = "今天是星期日";  
} else if (week == 1) {  
        str = "今天是星期一";  
} else if (week == 2) {  
        str = "今天是星期二";  
} else if (week == 3) {  
        str = "今天是星期三";  
} else if (week == 4) {  
        str = "今天是星期四";  
} else if (week == 5) {  
        str = "今天是星期五";  
} else if (week == 6) {  
        str = "今天是星期六";  
}  
return str；
}

第二版，换一种方式,用switch

​​​​​​​_getWeek = (str) => {
    var week=""; //存储星期几
             switch (new Date(str).getDay()) {
                         case 0:
                             week = "星期日";
                             break;
                         case 1:
                            week = "星期一";
                             break;
                         case 2:
                             week = "星期三";
                             break;
                         case 3:
                             week = "星期日";
                             break;
                         case 4:
                             week = "星期四";
                             break;
                         case 5:
                             week = "星期五";
                             break;
                         case 6:
                             week = "星期六";
                             break;
                         default:
                             week = "未知";
                             break;
                     }
                     return week;
}

第二版，比较简便

var a = new Array("日", "一", "二", "三", "四", "五", "六");  
var week = new Date().getDay();  
var str = "今天是星期"+ a[week];  
alert(str);  

第三版 更简便

var str = "今天是星期" + "日一二三四五六".charAt(new Date().getDay());alert(str);