Ajax Bestiary: A Javascript Field Guide
 
Ajax Bestiary: A Javascript Field Guide
 
 

Implicit Vs. Explicit Conversion in Javascript

January 14th, 2008 Posted by Don Albrecht

A question emerged out of my boredom on my flight yesterday.  Which is faster, implicit vs explicit conversion.  Most javascript developers use implicit conversion out of habit. For example:

!!x; instead of Boolean( x ); and x + “”; instead of String( x);. 

I decided to try an experiment for myself and record the performance of casting a number to a Boolean or String on my Windows box in Safari 3, Firefox 2, Opera 9 and IE 7.

The Verdict:

Implicit conversion wins handily, demonstrating over a 7 fold performance increase in one test. Overall, the performance gain for using implicit conversion averaged out to 53% across browsers after 10 tests.

The Numbers:

  Implicit Boolean Explicit Boolean Implicit String Explicit String
Firefox 2 0.162 0.312 0.248 0.358
IE 7 0.042 0.100 0.074 0.152
Opera 9 0.030 0.088 0.020 0.142
Safari 3 0.028 0.036 0.074 0.100
Cross Browser Average 0.066 0.134 0.104 0.188

You can find the code I used after the jump.

The Code:

<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01 Transitional//EN”>
<html>
  <head>
  <meta http-equiv=”content-type” content=”text/html; charset=windows-1250″>
  <meta name=”generator” content=”PSPad editor, www.pspad.com”>
  <title></title>
  <script type=”text/javascript”>
  // JavaScript Document

var implicitBoolean, explicitBoolean, implicitString, explicitString, startDate, endDate;

implicitBoolean = explicitBoolean = implicitString = explicitString = 0;

for( i = 0; i < 500; i++ ){

startDate= new Date();
for( i=0; i < 32000; i++){ Boolean( i );}
endDate = new Date();
explicitBoolean += ( endDate – startDate );
startDate= new Date();
for( i=0; i < 32000; i++){ !!i;}
endDate = new Date();
implicitBoolean += ( endDate – startDate );

startDate= new Date();
for( i=0; i < 32000; i++){ String( i );}
endDate = new Date();
explicitString += ( endDate – startDate );

startDate= new Date();
for( i=0; i < 32000; i++){ i + “”;}
endDate = new Date();
implicitString += ( endDate – startDate );
}

document.writeln( “Implicit Boolean:  ” + (implicitBoolean / 500 ) + “<br />” );
document.writeln( “Explicit Boolean:  ” + (explicitBoolean / 500 ) + “<br />” );
document.writeln( “Implicit String:  ” + (implicitString / 500 ) + “<br />” );
document.writeln( “Explicit String:  ” + (explicitString / 500 ) + “<br />” );
  </script>
  </head>
  <body>

  </body>
</html>


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