I am working on js to compare the performance of brute force O(n^2) and Barnes-Hut O(nlog(n))

In my code right now I am doing the same thing with the same data five times

like this:

let data = [arrays of 100 data];
let count = 5;
while(count>0){
  count--;
  console.time('brute force time' + iterationCount);
  brute force function()
  console.timeEnd('brute force time' + iterationCount);

  console.time('BH time' + iterationCount );
  Barnes Hut algorithm();
  console.timeEnd('BH time' + iterationCount);
 }
}

Though, the code is the same for each time, console.time is showing the different and worrying results.

In the timing, the difference between BH and brute force is not relatively similar in multiple iterations. and it is not predictable when I run code every time.

One more thing to notice is that every time I run the code, in the first iteration brute force and Barnes Hut algorithm timing are almost similar where as after first, it shows that Barnes-Hut is way better.

PS: everything in both functions is scoped to each function i.e local variable and shares the same data in each iteration so in each iteration code is identical !!!!

can anyone help me understand why I am getting like this?