A customized swap fails in bubbleSort

Question

I wrote such a swap function for bubbleSort:

function swap(a, b) {
    tmp = a;
    a = b;
    b = tmp;
}

then encapsulate it in the bubbleSort:

function bubbleSort(arr) {
    let len = arr.length;
    for (let i = 0; i < len; i++) {
        for (let j = 0; j < len - 1; j++) {
            // swap the elements
            if (arr[j] > arr[j + 1]) {
                swap(arr[j], arr[j + 1]); // use swap here.
            }
        }
    }
}

And test it with:

arr = [34, 87, 21, 0, -11];
bubbleSort(arr)

but it stay unchanged, what's the problem?

Answer 1

The swap function takes a copy of the number instead of the pointer.. welcome to javascript?
Either way, you would need the array and the indexes to do a swap because objects are pointers, numbers are not
Here's an example

//working swap function
function swap(arr, a, b){
  var tmp=arr[a]
  arr[a]=b
  arr[b]=tmp
}

function bubbleSort(arr) {
    let len = arr.length;
    for (let i = 0; i < len; i++) {
        for (let j = 0; j < len - 1; j++) {
            // swap the elements
            if (arr[j] > arr[j + 1]) {
                swap(arr, j, j+1); // use swap here.
            }
        }
    }
    return arr //because why not
}

arr = [34, 87, 21, 0, -11];
console.log(bubbleSort(arr))