gistfile1.js

function BenchmarkRun() {
  // Benchmark.prototype.setup goes here
  obj = {
   "apples": true,
   "oranges": true,
   "pears": true,
    "pinapples": true,
    "grapes": true,
  }
  array = [
    "apples",
    "oranges",
    "pears",
    "pinapples",
    "grapes",
  ]
  
  var start = new Date;
  for (...) { // do N iterations of test body
    delete obj.pears
  }
  var end = new Date;
  // Performance is expressed in runs per second: N / ((start - end) / 1000)
  // But notice how only the first run of the loop actually deletes something
  // at subsequent iterations property has been already deleted. Which makes
  // resulting metrics reflect more "how much does it cost to *not* delete a property"
  // then what you really wanted to measure
};