javascript - How to splice an element to the start of an array?

I'm new to Javascript and I'm trying to create a function that rotates the array depending on how many times num is === to. So if num = 2 ["Harry", "Sarah", "Oscar", "Tina"] becomes ["Oscar", "Tina", "Harry", "Sarah"]

Here is my code so far:

var count = 0;


function rotate(arr, num) {
  while (count < num) {
    arr.splice(0,0, "Tina");
    arr.pop();
    count++
  }
  return arr
}

console.log(rotate(["Harry", "Sarah", "Oscar", "Tina"], 2));

For this Line - arr.splice(0,0, "Tina"); I want it to be so that it will bring whatever name is the fourth element to the front of the array, I'm not sure if this is possible? I am suppposed to do this method using splice. Thanks for any help?! :)

Edit: This question is different to other questions. I don't want a full blown solution for rotation, I just want to know if it's possible to splice the fourth element to the beginning?

Answer

Try shifting the array in a for loop:

function rotate(arr, num){
    for(var i = 0; i < num; i++){
        item = arr[arr.length-1]
        arr.splice(arr.length-1, 1);
        arr.unshift(item)
    }
    return arr
}

alert(JSON.stringify(rotate(["Harry", "Sarah", "Oscar", "Tina"], 2)));

alert(JSON.stringify(rotate(["Harry", "Sarah", "Oscar", "Tina"], 1)));