JavaScript - 使用数组索引转换为字符串

Question

我从一本书上得到了这段代码，但我不明白这个语句“mm=months[mm]”如何转换为月份名称字符串:

function init(){
    var panel = document.getElementById("panel");

    var days=["sun","mon","tue","wed","thur","fri","sat"];
    var months=["jan","feb","mar","apr","may","jun",
    "jul","aug","sep","oct","nov","dec"];

    var now = new Date();

    var yy = now.getFullYear();
    var mm = now.getMonth();
    var dd = now.getDate();
    var dy = now.getDay();

    mm=months[mm];  //convert to month name string
    dy=days[dy];  //convert to month name string

    var str = dy+","+mm","+dd+","+yy;
    panel.innerHTML+="us date string: "+str;
    str = dy+","+dd+" "+mm+","+yy;
    panel.innerHTML+="<br>uk date string: "+str;
}
window.onload=init();

我的问题是 mm=months[mm] 和 dy=days[dy] (转换为月份或日期名称字符串)到底是做什么的。我不明白当月份是一个数组时，这个语句“mm=months[mm]”如何转换为月份名称字符串。这只是数组的一些内置函数吗？

Answer 1

mm 是语句 mm=months[mm] 开头的数字，因此它返回中的第 mm 值months 数组，它是一个字符串。在 JavaScript 中，变量的类型并不严格，因此它会将此字符串插入变量 mm