There's a small mistake in your code. The splice method modifies the array in place and returns an array containing the deleted elements. You need to insert one array into another, so all you need is a single splice. Here is the modified version of code:
function frankenSplice(arr1, arr2, n) {
let newarr = arr2.slice();
newarr.splice(n, 0, ...arr1);
console.log(arr2);
console.log(newarr);
return newarr;
}
frankenSplice([1, 2, 3], [4, 5, 6], 1);
Reference:
https://stackoverflow.com/questions/58209968/how-to-use-splice-and-slice-to-put-an-array-into-another-array[
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