jstests/native_vs_custom_Array_isArray_perf_test.html at master · kreshano/jstests · GitHub

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
  "http://www.w3.org/TR/html4/strict.dtd">
<html>
  <head>
    <meta http-equiv="Content-type" content="text/html; charset=utf-8">
    <title></title>
  </head>
  <body>
    <p style="font-size:1.5em;font-weight:bold;">Testing performance of native <code>Array.isArray</code> vs custom implementation <br>(i.e. <code>Object.prototype.toString.call(object) === "[object Array]"</code>)</p>
    <script type="text/javascript">
      (function(){

        if (!Array.isArray) {
          return document.write('No `Array.isArray` detected');
        }

        function customIsArray(o) {
          return toString.call(o) === '[object Array]';
        }
        function getAverage(values) {
          var sum = 0;
          for (var i = values.length; i--; ) {
            sum += values[i];
          }
          return sum / values.length;
        }

        var arr = [ ],
            nonArr = { },
            toString = Object.prototype.toString,
            lim = 50000,
            tries = 10,
            t,
            results = [ ];

        results.length = 0;
        for (var j = tries; j--; ) {
          t = new Date();
          for (var i = lim; i--; ) {
            Array.isArray(arr);
            Array.isArray(nonArr);
          }
          results.push(new Date() - t);
        }
        var average1 = getAverage(results);

        results.length = 0;
        for (var j = tries; j--; ) {
          t = new Date();
          for (var i = lim; i--; ) {
            customIsArray(arr);
            customIsArray(nonArr);
          }
          results.push(new Date() - t);
        }
        var average2 = getAverage(results);

        document.write('Average of ' + tries + ' tries, ran ' + lim + ' times each <br><br>' +
          ' native: ' + average1 + 'ms; custom: ' + average2 + 'ms');
      })();
    </script>
  </body>
</html>