Run results for: Set.prototype.has() vs "in" operator

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Firefox/91.0

Browser: Firefox 91

Operating system: Mac OS X 10.15

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
Set.prototype.has()	265.0 Ops/sec
"in" operator	642.1 Ops/sec

Script Preparation code:

var set = new Set();
var obj = Object.create(null);

var test = (function (length, size, probability) {
  function random() {
    return Math.random().toString(36).substr(2);
  }
  var i;
  
  var array = [];
  array.length = size;
  for (i = 0; i < size; i++) {
    var str = random();
    set.add(str);
    obj[str] = true;
    array[i] = str;
  }
  
  var test = [];
  test.length = length;
  var c = size / probability;
  for (i = 0; i < length; i++) {
    var index = Math.floor(Math.random() * c);
    test[i] = index < size ? array[index] : random();
  }
  return test;
})(10000, 1000000, 0.5);

Tests:

Set.prototype.has()
var count = 0; for (var i = 0; i < test.length; i++) { if (set.has(test[i])) { count++; } }
"in" operator
var count = 0; for (var i = 0; i < test.length; i++) { if (test[i] in obj) { count++; } }