On Aug 28, 2008, at 12:14 PM, Dave Herman wrote:
> I interpreted Erik's point to be that the binding of `this' is not
> lexically scoped, so it would be useful to have a lexically scoped
> variable initially bound to the global object. IOW, if I write:
>
> this.print("blah blah blah")
>
> and then I refactor the code to say:
>
> (function() {
> this.print("blah blah blah")
> })()
>
> it breaks.
It happens not to break, because ES3 requires a null |this| for such
calls, where the null is later replaced by the global object.
obj = {
method: function () { this.print("blah blah blah"); },
print: function () { print("not the print you want"); }
};
obj.method();
would break, though.
We've been trying to fix the ES3 null->global rule for a while. Any
change is an incompatible change, but the current rule leads to
unintended global mutation and capture bugs.
> By contrast if I have a standard library binding `global'
> that's bound to the same thing as `this' at the top level, then I
> can write:
>
> global.print("blah blah blah")
>
> and the same refactoring:
>
> (function() {
> global.print("blah blah blah")
> })()
>
> continues to work the same. But there's no need for a special
> keyword or
> anything like that.
Indeed, Doug Crockford proposed at the January TC39 meeting this year
to make 'this' act like a lexically bound variable, with the only
magic to it applying to the case of obj.method() call expressions
(and variatons, obj[name] where name = 'method'), where 'this' would
be overridden -- if you will, a shadowing 'this' would be bound to obj.
I liked Doug's proposal quite a bit. I do not see anything like it in
ES3.1, but I'd like to see it in Harmony.
/be
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