Find array index equal element - javascript code written, study code for me to learn JavaScript

FindArrayIndexEqualElement.js

/*
  Binary Search Approach: O(logN)
   0   1   2   3   4   5   6 
  [0, 1,  2,  4,  5,  6,  10]
    
    l          m           h           
    l  m        h
    
 Do Binary search until lo is greater than hi
    
  mid = Math.floor(lo + hi);
  - if element is equal to it's index, return index
  - else if the element is greater than it's index value
    hi = mid - 1
  - else
    lo = mid + 1    
*/

function indexEqualsValueSearch(arr) {
  
  let lo = 0;
  let hi = arr.length - 1;
  let mid;
  
  while (lo <= hi) {
    mid = Math.floor((lo + hi)/2);
    
    if (arr[mid] === mid) {
      let leftPartition = arr.slice(lo, mid);  // exclude mid -> 
      let leftResult = indexEqualsValueSearch(leftPartition);
      
      if (leftResult === -1) {
        return mid;
      }
      return leftResult;
    }
    else if (arr[mid] > mid) {
      hi = mid - 1;
    }
    else {
      lo = mid + 1;
    }
  }
  
  return -1;  
}

let arr1 = [0, 1,  2,  4,  5,  6,  10];
let arr2 = [-8,0,2,5];
let arr3 = [-1,0,3,6];

console.log(indexEqualsValueSearch(arr1)); // 0
console.log(indexEqualsValueSearch(arr2)); // 2
console.log(indexEqualsValueSearch(arr3)); // -1