Sums of Parts challenge

I am solving Sums of Parts challenge by codewars platform. I think that I solved the challenge but I still need to deal with arrays have thousands of elements.

My code:

function partsSums(ls) {
    let length = ls.length;
    let newArr = [ls.reduce((acc, cur) => acc + cur, 0)];
    for (let i = 0; i < length; i++) {
        ls.splice(0, 1);
        newArr.push(ls.reduce((acc, cur) => acc + cur, 0))
    }
    return newArr;
}

console.log(partsSums([1, 2, 3, 4, 5, 6]))`

The link of the challenge:

What is your question?

My question is What to do to deal with big elements in array?

for example:

partsSums([
  20, 7, 18, 20, 20, 16, 35,
  10, 7, 12, 36, 13, 22,  7,
  15, 7, 17, 22, 20, 19
])