splice:從數組中刪除或是取代，數量。

參數（第一個參數,數量,數據）
第一個參數可以是字串，數字，
第二個參數一定是數量：0～…
第三個參數可以是字串，數字：如果有為取代，如果沒有為新增

刪除

const arr =["apple","book","phone"]
const arrSplice=arr.splice("apple",1);
console.log('arrSplice',arrSplice);
//arrSplice ["apple"]
console.log('arr',arr);
//arr ["book","phone"]

取代

const arry =["apple","book","phone"];
const  arrySplice=arry.splice("apple",1,"spack");
console.log('arrySplice',arrySplice);
//"arrySplice" ["apple"]
console.log('arry',arry);
//"arry" ["spack","book","phone"]

新增

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2,0,"Lemon","Kiwi");
console.log('fruits',fruits);
//"fruits" ["Banana","Orange","Lemon","Kiwi","Apple","Mango"]