copyWithin() 方法用於從數組的指定位置拷貝元素到數組的另一個指定位置中。
返回修改後的數組(即直接修改原數組),不會改變數組的長度
array.copyWithin(target, start, end)target爲必需,複製到指定位置目標索引,可以爲負值,爲負值後,索引爲length+target
start 可選,元素複製的起始位置,省略,默認爲0。可以爲負值,爲負值後,索引爲length+start
end 可選,省略,默認爲數組的length,可以爲負值,爲負值後,索引爲length+end
若start的值大於end,則直接返回原數組,不進行任何處理
var arr = ["apple","banana","cover","double"];
arr.copyWithin(1,2,1)
=> Array [ "apple", "banana", "cover", "double" ]
start和end是先進行比較大小,然後在進行負值處理,
var arr = [ "apple", "banana", "cover", "double" ]
arr.copyWithin(1,-1,-2)
Array [ "apple", "banana", "cover", "double" ]