Assigning to globals in strict mode

Dmitry A. Soshnikov dmitry.soshnikov at gmail.com
Mon Oct 18 00:57:20 PDT 2010


  On 18.10.2010 1:56, Oliver Hunt wrote:
> I'm just in the process of making jsc produce the correct error in strict mode when assigning to an undefined priority, and I just want to verify my understanding of the spec (which is somewhat confused by multiple people stating that in strict mode the assignment operator can never create a new global property).
>
> Per section 11.13.1 an implementation should throw a syntax error if LeftHandSideExpression evaluates to an unresolvable reference, which means
>
> "use strict"; undeclared = (this.undeclared = 5);
>
> Should throw as |undeclared| will not exist when LeftHandSideExpression is evaluated.
>

As far as I can see, yeah, it's a ReferenceError. However, it will be 
more logical not to have it (because of grouping operator which 
logically assumes precedence). The situation can be corrected if to 
exchange first and the second steps of the 11.13.1.

> Similarly
>
> "use strict"; this.declared = 5; declared = (delete declared, 5);
>
> Will not throw, but instead will recreate the |declared| property.
>

Following 8.7.2, it will also throw because of step 3. However, this 
case (in contrast with the previous with assignment) looks more logical, 
'cause grouping operator assumes that this action should be made first. 
That is, we have first deleting of the `declared`, and then trying to 
assign 5 to undeclared `declared`.

So to make the first case more logical, I propose to change 1st and 2nd 
steps of the 11.13.1:

1. Let rref be the result of evaluating AssignmentExpression.
2. Let lref be the result of evaluating LeftHandSideExpression.

and to add a small note, clarifying for what it is needed.

Dmitry.

> I'm simply wanting to verify my interpretation of the spec prior to fixing this bug.
>
> --Oliver
>
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