在javascript数组中使用两个括号是什么意思

Question

我想在javaScript中更改日期格式，并且我发现这个代码非常好，“Mike Christensen”。 但我的问题是关于什么是在JavaScript阵列码在VAR月线3含义使用两种支架。

var mydate = new Date(form.startDate.value); 
var month = ["January", "February", "March", "April", "May", "June", 
"July", "August", "September", "October", "November", "December"] [mydate.getMonth()]; 
var str = month + ' ' + mydate.getFullYear(); 

Answer 1

他是用他得到它从mydate.getMonth月号（）

在此代码

这里，mydate.getMonth（）是11和在他本月索引数组索引月份阵列一个月[11]将在12月

var mydate = new Date(); 
 
console.log(mydate.getMonth()); 
 
var month = ["January", "February", "March", "April", "May", "June", 
 
"July", "August", "September", "October", "November", "December"] [mydate.getMonth()]; 
 
console.log(month); 
 
var str = month + ' ' + mydate.getFullYear();

希望你能理解

Answer 2

第一对括号的是创建阵列，可以考虑像这样

var month = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"] 

下一对括号的是用于通过索引阵列检索操作。

someArr[index] 

你的情况

month[11] 

就是这样，笔者只是指数，其中指数是从另一个变量中提取拿刚刚创建数组的元素。

Answer 3

这样做：就是给init VAR一个月以前声明数组中的元素只有一个非常廉价的方式...（东西会节省你写一行多个但恕我直言降低代码的可读性... ） 所以断裂下来：

var month = ["January", "February", "March", "April", "May", "June", 
"July", "August", "September", "October", "November", "December"] [mydate.getMonth()]; 

相同

var monthOptionsArray = ["January", "February", "March", "April", "May", "June", 
"July", "August", "September", "October", "November", "December"]; 

var monthIndex = mydate.getMonth(); 
var monthActual = monthOptionsArray[monthIndex]; 

实施例：

var mydate = new Date(); 
 
console.log(mydate.getMonth()); 
 
var month = ["January", "February", "March", "April", "May", "June", 
 
"July", "August", "September", "October", "November", "December"]; monthI = month[1]; 
 
console.log(monthI); 
 
var str = month + ' ' + mydate.getFullYear();