在给定索引 n 处将 arr1 复制到 arr 2，并且在 function 运行后 arr 1 和 arr2 应该相同

Question

I am trying to copy arr1 to arr 2 at given index n and arr 1 and arr2 should be same after function runs. So I have put a = arr2 and operate on a but arr2 is also changing

 function frankenSplice(arr1, arr2, n) { let a = arr2 console.log(a) a.splice(n,0,...arr1); console.log(arr2) return a } console.log(frankenSplice([1, 2, 3], [4, 5, 6], 1));

Answer 1

Arrays in javascript are mutable, so when you use

let a = arr2

array a becomes arr2 , and when you modify one, you modify both (beacuse they are essentialy the same array)

To solve your problem, you can use spread operator to copy content of your original array to the new one, so it would look like this

let a = [...arr2]

Answer 2

You need to make a a copy of arr2 , one way to do that would be to use slice :

 const frankenSplice = (arr1, arr2, n) => { const a = arr2.slice(0); // 0 is not required but makes it slightly faster a.splice(n, 0, ...arr1); return a } const arr1 = [1, 2, 3]; const arr2 = [4, 5, 6]; console.log(frankenSplice(arr1, arr2, 1)); console.log(arr1); console.log(arr2);

Answer 3

Using flatMap should make simplify for this case.

 function frankenSplice(arr1, arr2, n) { return arr2.flatMap((num, i) => (i === n? [...arr1, num]: num)); } console.log(frankenSplice([1, 2, 3], [4, 5, 6], 1));