On 07.09.2011 15:21, Dmitry Pashkevich wrote:
On Wednesday, September 7, 2011 2:57:17 PM UTC+4, Dmitry A. Soshnikov
wrote:
And this variable is not read-only, you may assign to it
(*while cannot to function's name*).
But I can do this:
function x() {};
x = 123;
x; // 123
Right, because in this case you create a FD (function declaration) which
name "x" becomes the name of a binding in the environment -- without
read-only attribute (though, it's non-configurable, as well as other
vars -- that is, you can't delete them). Schematically:
TheGlobalEnvironment = {
x: <reference to function "x">,
// other bindings incl. built-ins
};
And because JS is a dynamic and mutable language, you may of course
re-assign the "x" binding to new value:
x = 123; // TheGlobalEnvironment.x = 123
But in case of a NFE (named function expression) a _special object_
object is created which stores the binding of the function's name. And
this binding is _immutable_. Thus, this special object is inserted
_before_ the environment, thus just _shadowing_ the name of a binding
with the same name in the environment:
Let's say you have:
var x = function x() {
x = 123;
alert(x);
};
then:
1. Global "x" binding is created and attached to the result of (3)
2. Special object is created with a single property "x" -- the name of a
function
3. A function is created which gets its scope chain as SpecialObject +
TheGlobalEnvironment: {x: function, ReadOnly: true} -> {x: function,
ReadOnly: false}
and then, when you refer "x" from the body of the function, of course
the first "x" is found -- that is in this specially created object to
store the reference to the function -- only for the time a function is
executed.
Dmitry.
I just can't understand the environment that takes place when the code
inside the function executes (in the original post)
!function x(){*x=123;alert(x);*}()
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