One of the complaints about prototype.js (google for it if you're not
familiar with it) is that it's poorly documented. I have this inkling
that the key to understanding prototype.js is in the bind function.
The problem with Javascript is that the "this" operator is poorly
overloaded and it is often hard to understand in the context of
object-oriented javascript
So, let's start with the definition:
Function.protot ype.bind = function(object ) {
var method = this;
return function() {
method.apply(ob ject, arguments);
}
}
As I read this, it states that all functions (which are themselves
objects) will, in the future, have an associated method called "bind".
The function() function, so to speak, simply instantiates a Function
object with the parameter list and then evals the statement, sticking
the resulting execution-tree in the current code frame.
The "this" there refers to the function object associated with the call
to bind(), right? But the word "arguments" there refers to the
arguments passed to the function object *generated by* the call to
bind().
In every example within prototype.js, bind() is called either in a
constructor or within a method contexted to a javascript object, and is
always called with "this" as its argument, e.g.:
this.options.on Complete = this.updateCont ent.bind(this);
As I read the code it seems to be stating that the "this" object
referred to within bind()'d functions are being coerced into always
referring to the current instantiated object.
But isn't this always the case anyway? Is this a rather confusing
attempt to ensure "this" purity whereby the call
method.apply(ob ject, arguments)
is forced to always have the reference to the containing object present?
I think I've got it. Bind() generates uniq functions that contain live
references to the objects to which they belong, such that the function
object can then be passed to setTimeout() or onMouseOver(), handlers
that accept functions but not objects.
Have I got this right?
Elf
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