Re: making |this| an error (was Re: for own(...) loop)
2011/11/9 John J Barton
> I'm sure this has been discussed before, but isn't is possible and
> desirable to make |this| illegal in "using strict;" when it can be
> determined from the AST alone that |this| will bind to |window|? eg:
>
> Object.keys(foo).forEach(function(key) {
> // this is undefined-> window
> });
>
> This case kind of case is because, as others have noted, incorrect
> |this| binding most often occurs in two cases: 1) mixed OO and
> functional programming (as above) and 2) callback defn.
>
>
In `strict-mode', |this| would resolve to `undefined' inside that function
anyways. I'm not a fan of making constructs "illegal" just because
their semantics might be confusing, even more so when such
disallowance would vary highly in context. It would be bound to
make things more confusing, imho.
Block lambdas are the best solution I can see right now.
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Re: making |this| an error (was Re: for own(...) loop)
On Wed, Nov 9, 2011 at 7:22 AM, Peter van der Zee wrote:
> The forEach method might not do what you expect it to. This can not be
> statically determined.
And if forEach is not what you expect, that function may bind its argument:
foo(function() {
do something with |this|
});
function foo(fn) { bar.fn()};
I suppose it's more of a lint thing then.
jjb
>
> - peter
>
> On 9 Nov 2011 16:10, "John J Barton" wrote:
>>
>> On Wed, Nov 9, 2011 at 3:41 AM, David Bruant wrote:
>> > Le 09/11/2011 02:26, Andrew Paprocki a écrit :
>> >>
>> >> On Tue, Nov 8, 2011 at 6:36 PM, Brendan Eich
>> >> wrote:
>> >>>
>> >>> Ignoring performance, a lot of stylish JS hackers use
>> >>> Object.keys(o).forEach. How many run into the wrong |this|
>> >>> (arguments/break/continue/return)? Not clear. Something to study.
>> >>
>> >> I was curious so I did some grok-ing across my code sample and
>> >> Object.keys() is barely used. The usage of the |for in| construct is 2
>> >> orders of magnitude larger than the usage of hasOwnProperty(),
>> >> supporting the thought that no one really does it the "right" way.
>> >>
>> >> The MDN page for Object.keys does not talk about |this| being wrong in
>> >> certain situations. If you could elaborate on that, it would be
>> >> helpful to know.
>> >
>> > The |this| differs between the body of a for-in and the argument
>> > callback in
>> > the .forEach. Nothing to do with Object.keys. .forEach has a second
>> > optional
>> > argument which is the value to be used as |this| so that you don't have
>> > to
>> > do a .bind.
>>
>> I'm sure this has been discussed before, but isn't is possible and
>> desirable to make |this| illegal in "using strict;" when it can be
>> determined from the AST alone that |this| will bind to |window|? eg:
>>
>> Object.keys(foo).forEach(function(key) {
>> // this is undefined-> window
>> });
>>
>> This case kind of case is because, as others have noted, incorrect
>> |this| binding most often occurs in two cases: 1) mixed OO and
>> functional programming (as above) and 2) callback defn.
>>
>> Perhaps it is harder to detect than I think.
>>
>> jjb
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>> es-discuss@mozilla.org
>> https://mail.mozilla.org/listinfo/es-discuss
>
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Re: making |this| an error (was Re: for own(...) loop)
On 9 November 2011 16:10, John J Barton wrote:
> I'm sure this has been discussed before, but isn't is possible and
> desirable to make |this| illegal in "using strict;" when it can be
> determined from the AST alone that |this| will bind to |window|? eg:
>
> Object.keys(foo).forEach(function(key) {
> // this is undefined-> window
> });
How do you know statically that `this' would be undefined? Somebody
might have modified forEach.
In JavaScript, you generally don't know a whole lot of things statically.
/Andreas
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Re: making |this| an error (was Re: for own(...) loop)
The forEach method might not do what you expect it to. This can not be
statically determined.
- peter
On 9 Nov 2011 16:10, "John J Barton" wrote:
> On Wed, Nov 9, 2011 at 3:41 AM, David Bruant wrote:
> > Le 09/11/2011 02:26, Andrew Paprocki a écrit :
> >>
> >> On Tue, Nov 8, 2011 at 6:36 PM, Brendan Eich
> wrote:
> >>>
> >>> Ignoring performance, a lot of stylish JS hackers use
> >>> Object.keys(o).forEach. How many run into the wrong |this|
> >>> (arguments/break/continue/return)? Not clear. Something to study.
> >>
> >> I was curious so I did some grok-ing across my code sample and
> >> Object.keys() is barely used. The usage of the |for in| construct is 2
> >> orders of magnitude larger than the usage of hasOwnProperty(),
> >> supporting the thought that no one really does it the "right" way.
> >>
> >> The MDN page for Object.keys does not talk about |this| being wrong in
> >> certain situations. If you could elaborate on that, it would be
> >> helpful to know.
> >
> > The |this| differs between the body of a for-in and the argument
> callback in
> > the .forEach. Nothing to do with Object.keys. .forEach has a second
> optional
> > argument which is the value to be used as |this| so that you don't have
> to
> > do a .bind.
>
> I'm sure this has been discussed before, but isn't is possible and
> desirable to make |this| illegal in "using strict;" when it can be
> determined from the AST alone that |this| will bind to |window|? eg:
>
> Object.keys(foo).forEach(function(key) {
> // this is undefined-> window
> });
>
> This case kind of case is because, as others have noted, incorrect
> |this| binding most often occurs in two cases: 1) mixed OO and
> functional programming (as above) and 2) callback defn.
>
> Perhaps it is harder to detect than I think.
>
> jjb
> ___
> es-discuss mailing list
> es-discuss@mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
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Re: making |this| an error (was Re: for own(...) loop)
On Wed, Nov 9, 2011 at 3:41 AM, David Bruant wrote:
> Le 09/11/2011 02:26, Andrew Paprocki a écrit :
>>
>> On Tue, Nov 8, 2011 at 6:36 PM, Brendan Eich wrote:
>>>
>>> Ignoring performance, a lot of stylish JS hackers use
>>> Object.keys(o).forEach. How many run into the wrong |this|
>>> (arguments/break/continue/return)? Not clear. Something to study.
>>
>> I was curious so I did some grok-ing across my code sample and
>> Object.keys() is barely used. The usage of the |for in| construct is 2
>> orders of magnitude larger than the usage of hasOwnProperty(),
>> supporting the thought that no one really does it the "right" way.
>>
>> The MDN page for Object.keys does not talk about |this| being wrong in
>> certain situations. If you could elaborate on that, it would be
>> helpful to know.
>
> The |this| differs between the body of a for-in and the argument callback in
> the .forEach. Nothing to do with Object.keys. .forEach has a second optional
> argument which is the value to be used as |this| so that you don't have to
> do a .bind.
I'm sure this has been discussed before, but isn't is possible and
desirable to make |this| illegal in "using strict;" when it can be
determined from the AST alone that |this| will bind to |window|? eg:
Object.keys(foo).forEach(function(key) {
// this is undefined-> window
});
This case kind of case is because, as others have noted, incorrect
|this| binding most often occurs in two cases: 1) mixed OO and
functional programming (as above) and 2) callback defn.
Perhaps it is harder to detect than I think.
jjb
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