Global Variables vs Local Variables (v43)

Revision 43 of this benchmark created by Brewster on

Description

This test compares the performance of global variables to local variables within functions.

Global variables should be slower because they do not exist in a function's activation object. JavaScript must traverse the Scope Chain to locate global variables.

Preparation HTML

<script>
  var a,b=0;
  function x() {
    for(a=0;a<20;a++)
      b+=a;
  }

  function w() {
    for(window.a=0;window.a<20;window.a++)
      window.b+=window.a;
  }

  function v() {
    var w = window;
    for(w.a=0;w.a<20;w.a++)
      w.b+=w.a;
  }

  function u() {
    var w = window, a = w.a, b = w.b;
    for(a = 0; a<20; a++)
      b += a;
  }

  function y() {
    var c,d=0;
    for(c=0;c<20;c++)
      d+=c;
  }
  function z(){
    var c = a,
        d = b;

    for(c=0;c<20;c++)
       d+=c;
  }
</script>

Test runner

Ready to run.

Testing in
TestOps/sec
Global variables
for(a=0;a<20;a++)
  b+=a;
ready
Local variables
var c,d=0;
    for(c=0;c<20;c++)
      d+=c;
ready
Cached global variables
var c = a,
    d = b;

for(c=0;c<20;c++)
   d+=c;
ready
Window
for(window.a=0;window.a<20;window.a++)
  window.b+=window.a;
ready
Cached window
var w = window;
for(w.a=0;w.a<20;w.a++)
  w.b+=w.a;
ready
Cached window and cached globals
var w = window, a = w.a, b = w.b;
for(a = 0; a<20; a++)
  b += a;
ready

Revisions

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