Have the scope accessible as an object and implement a new with operator / block
Hi,
There is this one thing in JavaScript I really hate: You can't so
{{$varName}} as in PHP so as soon as you need dynamic names, you have
to put everything in an object...
I don't know how scopes are implemented but there should be a not so
hard way to make them available as JS objects. The same way window
(or global or self or whatever) works for the global scope. Something
like this:
var a = { };
var b = [ ];
window[ 'a' ] === a;// true
window[ 'b' ] === b;// true
( function ( ) {
var a = { };
var b = [ ];
scope[ 'a' ] === a;// - true
scope[ 'b' ] === b;// - true
}( ) );
And the scope would inherit the parent scope. Here (this code would be
inside the function:
var scope = Object.create( window, {
a: {
value: a,
enumerable: true,
writable: true,
configurable: true
},
// same with b
} );
About the properties:
- enumerable true seems obvious
- writable too, except for variable declared with const
- configurable, I'd say false since you cannot use delete on variables
declared with var. But if you want the same behavior as window, then
variables declared with var would have configurable=false and the ones
declared as properties of the scope would have configurable=true.
var a = { };
window.b = { };
console.log( delete a );// false
console.log( delete b );// true
console.log( a );// Object
console.log( b );// ReferenceError: b is not defined
I always though this behavior was strange but since it is and doesn't
bother anyone...
About security, maybe Object.getPrototypeOf should throw an error on
scopes. Because having a child scope change your variables could be
strange... But that would only be a problem for scripts made with
third-party scripts included in own scripts that declare fake
variables to remove access to some features:
( function ( ) {
var window, setTimeout, undefined;
( function ( ) {// this function is from third party. It got
inserted in this code to make it safer
// whatever but can't access setTimeout
).call( undefined );
}( ) );
And without Object.getPrototypeOf and scope:
( function ( ) {
var window, setTimeout, undefined;
( function ( ) {// this function is from third party. It got
inserted in this code to make it safer
Object.getPrototypeOf( Object.getPrototypeOf( scope )
).setTimeout( function( ) { }, 100 );// you can access setTimout
).call( undefined );
}( ) );
This might not seam that useful but when you think about the with
operator from ES 3, if you add this scope thing, it becomes easy to
make it work properly.
I don't know how we could call it but what it would do is setting the
inner scope to an object. So ALL variables in that block would be
the object's properties and it would remove any other variable.
Here is an example:
( function ( ) {
var a = 'a';
var b = 'b';
var o = {
b: 'B',
c: 'C'
};
// here, scope == { a: 'a', b: 'b', o: { b: 'B', c: 'C' } }
with ( o ) {
// /!\ scope is still the same!
// otherwise you would have no access to real variables
b;// 'B'
c;// 'C'
try {
a;
} catch ( e ) {
e;// ReferenceError: a is not defined
}
scope.a;// 'a'
scope.b;// 'b'
scope.c;// undefined
}
} )( );
What do you think?
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Re: Have the scope accessible as an object and implement a new with operator / block
2011/12/20 Xavier MONTILLET xavierm02@gmail.com:
Hi,
There is this one thing in JavaScript I really hate: You can't so
{{$varName}} as in PHP so as soon as you need dynamic names, you have
to put everything in an object...
I don't know how scopes are implemented
Not being able to get hold of the scope as an object enables important
optimizations and is a feature, not a bug.
--
Erik Corry
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Re: Have the scope accessible as an object and implement a new with operator / block
What kind of optimizations? The variable have to be in some kind of
structure and it should be possible to read it as an object the same
way you read it as variables...
The fact that the inheritance between scopes I spoke of would be
hard to implement because they keep a one level deep structure and
change it when they change scope would be understandable. But no being
able to read the structure seems strange to me.
On Tue, Dec 20, 2011 at 11:19 AM, Erik Corry erik.co...@gmail.com wrote:
2011/12/20 Xavier MONTILLET xavierm02@gmail.com:
Hi,
There is this one thing in JavaScript I really hate: You can't so
{{$varName}} as in PHP so as soon as you need dynamic names, you have
to put everything in an object...
I don't know how scopes are implemented
Not being able to get hold of the scope as an object enables important
optimizations and is a feature, not a bug.
--
Erik Corry
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Re: Have the scope accessible as an object and implement a new with operator / block
I would love to have something like Python’s locals(): http://docs.python.org/py3k/library/functions.html#locals It would not allow modifications, but it would still be very useful. -- Dr. Axel Rauschmayer a...@rauschma.de home: rauschma.de twitter: twitter.com/rauschma blog: 2ality.com ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Have the scope accessible as an object and implement a new with operator / block
On 20 December 2011 11:24, Xavier MONTILLET xavierm02@gmail.com wrote: What kind of optimizations? Optimizations such as putting variables in registers, putting variables on the stack, overlaying variables with disjoint life times, eliminating some variables entirely, minimizing closure environments, to name just a few. /Andreas ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Have the scope accessible as an object and implement a new with operator / block
Well what about you add an if that checks whether scope is used or not and if it is disables these optimizations? On Tue, Dec 20, 2011 at 11:46 AM, Andreas Rossberg rossb...@google.com wrote: On 20 December 2011 11:24, Xavier MONTILLET xavierm02@gmail.com wrote: What kind of optimizations? Optimizations such as putting variables in registers, putting variables on the stack, overlaying variables with disjoint life times, eliminating some variables entirely, minimizing closure environments, to name just a few. /Andreas ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Have the scope accessible as an object and implement a new with operator / block
In a way it would be like proxies: slow if used but doesn't change anything if you don't use them. On Tue, Dec 20, 2011 at 11:51 AM, Xavier MONTILLET xavierm02@gmail.com wrote: Well what about you add an if that checks whether scope is used or not and if it is disables these optimizations? On Tue, Dec 20, 2011 at 11:46 AM, Andreas Rossberg rossb...@google.com wrote: On 20 December 2011 11:24, Xavier MONTILLET xavierm02@gmail.com wrote: What kind of optimizations? Optimizations such as putting variables in registers, putting variables on the stack, overlaying variables with disjoint life times, eliminating some variables entirely, minimizing closure environments, to name just a few. /Andreas ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Have the scope accessible as an object and implement a new with operator / block
On 20 December 2011 11:51, Xavier MONTILLET xavierm02@gmail.com wrote: Well what about you add an if that checks whether scope is used or not and if it is disables these optimizations? That's what's done for things like the `arguments' object. And it's an ugly mess, in terms of semantics as well as implementation. I believe it's fair to say that it is widely considered a misfeature these days. (ES is moving away from it, as well as from the global object.) /Andreas ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
