Probably there are very good reasons but I reask the question : why
should the attempt to access a property of a variable equal to undefined
global property not return undefined global property ? (ie a way that
this works : if (a.b.c.d) {} when a,a.b, etc are not set)
This can be usefull when things get loaded asynchronously and then when
you don't know when it will be available (it does not happen every day,
but in some cases you don't have necessarily a callback or an event to
tell you and then asynchronous stuff can start being extremely difficult
to handle).
Example :
console.log(a);//Reference error, GetBase returns undefined
console.log(window.a);//undefined
--> does not seem very logical, no ?
Maybe it was discussed thousand of times, but why not :
8.9.1 GetValue (V)
...
5. If IsUnresolvableReference(V), return undefined
Le 15/06/2012 01:22, Allen Wirfs-Brock a écrit :
On Jun 14, 2012, at 3:49 PM, Rick Waldron wrote:
On Thu, Jun 14, 2012 at 5:35 PM, Thaddee Tyl <[email protected]
<mailto:[email protected]>> wrote:
On Thu, Jun 14, 2012 at 3:29 PM, Allen Wirfs-Brock
<[email protected] <mailto:[email protected]>> wrote:
> This is a different issue, but I wonder how badly the web would
break if we
> made undefined a reserved word. Does anybody in JS really
declare a
> different local binding for undefined? In ES5 we got away with
making
> undefined read-only. Maybe we should continue pushing and see
if we can
> eliminate the rebindable undefined hazard.
JQuery [1] famously has an "undefined" parameter, like so:
(function( window, undefined ) { ... }(window))
Actually, this exists because undefined wasn't reserved. We would
certainly remove the formal param in favor of an reserved undefined.
Unfortunately, we can't "take it back" in extant code.
A wonder if this wart is hairy enough, that we wouldn't be justified
in some explicit backwards compatibility hackery in the spec. to
remove it.
For example, we could allow it to appear in parameter lists and
provide a dynamic check to ensure that nothing (other than a real
undefined) is passed. Similarly we could explicitly allow:
var undefined;
Certainly there is no particular reasons we need to allow:
let undefined;
const undefined=true;
class undefined extends foo { }
or any other new binding forms redefining undefined.
Allen
Rick
What would happen in this case?
[1] http://code.jquery.com/jquery-1.7.2.js
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