Code

  function heap(arr) {
      start = 0;
      end = arr.length -1 ;
      for(let i=end;i>0;i--) {
          for(let j=Math.floor((i-1)/2);j>=0;j--) {
              let left = 2*j+1;
              let right = 2*j+2;
              let big = left;
              if(right <=i && arr[right]>arr[left]) {
                  big = right;
              }
              if(arr[j] < arr[big]) {
                  let temp = arr[big];
                  arr[big] = arr[j];
                  arr[j] = temp;
              }
          }
          let temp = arr[i];
          arr[i] = arr[0];
          arr[0] = temp;
      }
      return arr;
    }
                    

Complexity

Time Complexity:

Best Case : Ω (n log(n))
Average Case : θ (n log(n))
Worst Case: O (n log(n))

Space Complexity:

O(1)

** where n is the length of the array