CODEWITHSUNDEEP
javascriptperformancebenchmarking
user26732
user26732

Reputation: 3854

Why is running code single time slower than running four times in javascript

See code and benchmark here: http://jsperf.com/single-vs-multiple-times-2

I am seeing a strange behaviour in javascript. Running code single time is taking twice as much as running it multiple times. Following is the code:

Preparation code

var MakeKeyCodepoint = function() {};
MakeKeyCodepoint.prototype.makeKey = function(word) {
  var len = word.length;
  if (len > 255) {
    return undefined;
  }
  var i = len >> 2;
  return String.fromCharCode(
    (word.charCodeAt(0) & 0x03) << 14 |
    (word.charCodeAt(i) & 0x03) << 12 |
    (word.charCodeAt(i + i) & 0x03) << 10 |
    (word.charCodeAt(i + i + i) & 0x03) << 8 |
    len
  );
};
var makeKeyCodepointObj = new MakeKeyCodepoint();

Running single time

var key = makeKeyCodepointObj.makeKey('www.wired.com');

Running four times

var key = makeKeyCodepointObj.makeKey('www.wired.com');
key = makeKeyCodepointObj.makeKey('www.youtube.com');
key = makeKeyCodepointObj.makeKey('scorecardresearch.com');
key = makeKeyCodepointObj.makeKey('www.google-analytics.com');

I am running it in chrome 34 in osx.

Upvotes: 0

Views: 156

Answers (2)

Esailija
Esailija

Reputation: 140220

You need to fix your benchmark so that it actually does something: http://jsperf.com/single-vs-multiple-times-2/5

Should give exactly 4 times slower.

Upvotes: 0

workabyte
workabyte

Reputation: 3755

looks like you are benchmarking the operations per second, not the time for completion. running it more times at onces would have more operations to perform so your results seem reasonable

reviewing the revisions i would say that was an anomaly run and the result was likely longer due to website server response when you ran it

Revision 4 shows what i would expect to see

Upvotes: 1

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