let vs var performance (v50)

Revision 50 of this benchmark created on

Preparation HTML

<script>
  var sideffect;
  var firstarray = [];
  var secondarray = [];
  (function(){

    'use strict';
    for (var i = 0; i < 100; i++) {
      firstarray[i] = Math.floor(Math.random() * 11);
    }
    for (var i = 0; i < 100; i++) {
      secondarray[i] = Math.floor(Math.random() * 11);
    }
  })();
</script>
<script>
(function() {

  'use strict';
  function usingvar() {
    for (var i = 0; i < 100; ++i) {
      var firstnumber = firstarray[i];
      for (var j = 0; j < 200; ++j) {
        var secondnumber = secondarray[j%100] + 5;
        var total = firstnumber + secondnumber;
        sideffect = total;
      }
    }
    for (var i = 0; i < 100; ++i) {
      var firstnumber = firstarray[i];
      for (var j = 0; j < 200; ++j) {
        var secondnumber = secondarray[j%100] + 5;
        var total = firstnumber + secondnumber;
        sideffect = total;
      }
    }
  }
  window.usingvar = usingvar;
})();
</script>
<script class="usinglet" type="application/javascript;version=1.8">
(function() {

  'use strict';
  function usinglet() {
    for (let i = 0; i < 100; ++i) {
      let firstnumber = firstarray[i];
      for (let j = 0; j < 200; ++j) {
        let secondnumber = secondarray[j%100] + 5;
        let total = firstnumber + secondnumber;
        sideffect = total;
      }
    }
    for (let i = 0; i < 100; ++i) {
      let firstnumber = firstarray[i];
      for (let j = 0; j < 200; ++j) {
        let secondnumber = secondarray[j%100] + 5;
        let total = firstnumber + secondnumber;
        sideffect = total;
      }
    }
  }
  window.usinglet = usinglet;
})();
</script>
<script>
if ( !/Gecko\//.test(navigator.userAgent) ) {
  var script = document.querySelector('script.usinglet');
  script.removeAttribute('type');
  var parent = script.parentElement;
  parent.removeChild(script);
  parent.appendChild(script);
}
</script>

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Testing in
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var
usingvar();
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let
usinglet();
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