what is the wrong with this javascript function?

Question

I want to know what is wrong with this function that takes array and sums up it's elements

var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var sum = 0;
var arraySum = function() {
  for (var i = 0; i <= arr.length; i++) {
    sum += arr[i];
  }
  console.log(sum);
};
arraySum(arr);

Answer 1

You are trying to access an element outside of the array, this returns undefined.

for (var i = 0 ; i<= arr.length ; i++) {
//                 ^ the equal sign

replace it with

for (var i = 0 ; i< arr.length ; i++) {

var arr = [1,2,3,4,5,6,7,8,9,10];
var sum = 0;
var arraySum = function () {
    for (var i = 0; i< arr.length; i++) {
        sum += arr[i];
    }
};

arraySum(arr);
document.write(sum);