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:

   #

   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:

   #

   The with statement is especially expensive in IE.

3. 

   eyelidlessness said:

   #

   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:

   #

   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:

   #

   @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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