Subj : Re: "named" vs. anonymous function
To   : Jens Thiele
From : Brendan Eich
Date : Fri Dec 10 2004 02:20 pm

Jens Thiele wrote:
> Hi,
> 
> just out of curiousity:
> why do named functions have an additional prototype (in spidermonkey)?
> example:
> 


This is so that each function has the proper scope parent, yet we don't 
have to compile each time to get a new function for each dynamic scope. 
   Each dynamic scope, when activated, gets a clone of the 
compiler-created function object, whose __proto__ is that 
compiler-created funobj.

ECMA does not specify __proto__, so there's no way for a script to 
notice this difference.  It could notice that function object identity 
(== or ===) differs, but that's allowed by Edition 3 (search for "joined 
function object").

/be

> spidermonkey shell:
> 
> js> x=function foo(){}
> function foo() {
> }
> 
> js> y=function (){}
> function () {
> }
> 
> js> x.__proto__===Function.prototype
> false
> js> x.__proto__.__proto__===Function.prototype
> true
> js> y.__proto__===Function.prototype
> true
> 
> a graph perhaps better visualizing it:
> <http://egachine.berlios.de/named-vs-anon.png> (13k)
> 
> rhino does not do this:
> 
> js> x=function foo(){}
> function foo() {
> }
> 
> js> y=function (){}
> function () {
> }
> 
> js> x.__proto__===Function.prototype
> true
> js> y.__proto__===Function.prototype
> true
> 
> 
> Jens

.