Why is my code returning " [ undefined, undefined, undefined ]"?

Question

function sumAll(arr) {
  arr.sort();
  let lum = [];
  for (let i = arr[1]; i > arr[0]; i--) {
    lum.push(arr[i]);
  }
  return lum;
}

console.log(sumAll([1, 4]));

I want my code to do 4-3, then add the result to lum and so on until it reaches 1 but i'm stuck at this point. I don't know why it returns undefined.

Answer 1

You're pushing arr[i] onto the result:

lum.push(arr[i]);

So for example when i is 4 (because arr[1] is 4), what is the value arr[4] that you're pushing to the result? It's undefined in the array provided. I suspect you meant to just push i to the result?:

lum.push(i);

For example:

function sumAll(arr) {
  arr.sort();
  let lum = [];
  for (let i = arr[1]; i > arr[0]; i--) {
    lum.push(i);
  }
  return lum;
}

console.log(sumAll([1, 4]));