<script>
    'use strict';
    var start = performance.now();
    const x = 4;
    var y = 0;
    for (var i = 0; i < 10000000; i++)
      y += x + 2;
    var t = performance.now() - start;
    console.log(t);
    var start = performance.now();
    var x1 = 4;
    var y = 0;
    for (var i = 0; i < 10000000; i++)
      y += x1 + 2;
    t = performance.now() - start;
    console.log(t);
  </script>