在javascript數組中使用兩個括號是什麼意思

Question

我想在javaScript中更改日期格式，並且我發現這個代碼非常好，「Mike Christensen」。 但我的問題是關於什麼是在JavaScript陣列碼在VAR月線3含義使用兩種支架。

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

他是用他得到它從mydate.getMonth月號（）

在此代碼

這裏，mydate.getMonth（）是11和在他本月索引數組索引月份陣列一個月[11]將在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

第一對括號的是創建陣列，可以考慮像這樣

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

下一對括號的是用於通過索引陣列檢索操作。

someArr[index] 

你的情況

month[11] 

就是這樣，筆者只是指數，其中指數是從另一個變量中提取拿剛剛創建數組的元素。

Answer 3

這樣做：就是給init VAR一個月以前聲明數組中的元素只有一個非常廉價的方式...（東西會節省你寫一行多個但恕我直言降低代碼的可讀性... ） 所以斷裂下來：

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]; 

實施例：

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();