Perfection Kills

Foo = {
  Bar: {
    Baz: {
      Qux: {
        Quux: function(){}
      }
    }
  }
}

// Plain call
console.time('test');
    for (var i=0; i<100000; ++i) {
      Foo.Bar.Baz.Qux.Quux();
    }
console.timeEnd('test'); // 562 ms

// "with" outside the loop
console.time('test');
  with(Foo.Bar.Baz.Qux) {
    for (var i=0; i<100000; ++i) {
      Quux();
    }
  }
console.timeEnd('test'); // 359 ms

// with inside the loop
console.time('test');
for (var i=0; i<100000; ++i) {
  with(Foo.Bar.Baz.Qux) {
      Quux();
  }
}
console.timeEnd('test'); // 1891 ms

// aliasing
console.time('test');
  for (var i=0, q=Foo.Bar.Baz.Qux.Quux; i<100000; ++i) {
    q();
  }
console.timeEnd('test'); // 422 ms

Comments (5)

1. 

   fearphage said on Sep 9, 2007 @ 12:42

   #1

   Although this is similar, it is not actually using the with statement.

   with (Foo.Bar.Baz) {
for (var i = 0; i < 100000; i++) {
Quux();
}
}

2. 

   Tobie Langel said on Sep 11, 2007 @ 8:27

   #2

   The with statement is especially expensive in IE.

3. 

   eyelidlessness said on Dec 14, 2009 @ 13:34

   #3

   Reposted with <, > and & escaped…

   This is not testing the aspect of with() that is actually slow, which is when you reference objects in a with() block that are not in the object passed as an argument to with().

   var zig = function() {};
   
   console.time('test');
     with(Foo.Bar.Baz.Qux) {
       for (var i=0; i<1000000; ++i) {
         zig();
         Quux();
       }
     }
   console.timeEnd('test'); // 470ms (avg of 3)
   
   console.time('test');
     for (var i=0; i<1000000; ++i) {
       zig();
       Foo.Bar.Baz.Qux.Quux();
     }
   console.timeEnd('test'); // 438 ms (avg of 3)
   

   It’s not a huge difference, but it is a difference. With that said, the benefits of with() are greater if you are vigilant to only use properties descending from the object passed to with().

4. 

   eyelidlessness said on Dec 14, 2009 @ 13:37

   #4

   Well, it’s good to know that <pre> blocks are recommended for posting code sections, render great on the client-side preview, but are stripped when posted. That’s… helpful.

   http://i45.tinypic.com/2qnbn2f.jpg

5. 

   kangax (article author) said on Dec 14, 2009 @ 13:56

   #5

   @eyelidlessness

   Jeez, sorry about that, I fixed your comment. It worked fine last time I checked. Will need to see why they get stripped now.

   I’ll respond to a comment as soon as I get a chance.

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