HTML5 spec. seems to unnecessarily ban strict mode event handlers
rubys at intertwingly.net
Thu Feb 3 14:15:12 PST 2011
On 02/03/2011 05:00 PM, Allen Wirfs-Brock wrote:
> I was browsing Kangax's strict mode test result page
> (http://kangax.github.com/es5-compat-table/strict-mode/ ) and I
> noticed that he listed the recognition of a use strict directive of a
> event handler as a "non-standard" feature that he tests for. This
> spiked my curiosity as my recollection was the HTML5 event handler
> content attribute was specified to be text that is an ECMAScript
> FunctionBody. FunctionBody may contain a Directive Prologue that
> includes a use strict directive so, from an ECMAScript perspective,
> there shouldn't be anything non-standard about a strict mode event
> To be sure, I checked the event handler section of the HTML5 spec
> and to my surprise I discovered that it specifies the creation of the
> handler function in a manner that, at first glance, seems to
> explicitly cause the presence of a use strict directive to be
> ignored. Essentially it seems to specify that event handlers
> specified using the event handler attribute are never executed in
> ECMAScript 5 strict mode. I don't know whether or not this was
> intentional, but it certainly seems wrong. The "strictness" of an
> ECMAScript function is an internal and local characteristic of the
> function. For a ECMAScript host to say that a use strict directive
> is ignored is really no different from saying that IfStatements or
> any other syntactically valid element of a FunctionBody will be
> The HTML5 spec. get into this trouble because of the way it uses the
> abstract operation for creating function objects defined by section
> 13.2 of the ES5 specification
> In step 2 of the algorithm in HTML5 18.104.22.168 it unconditionally uses
> False as the Strict parameter to the ES5 13.2 algorithm. That might
> seem to exclude the function from strict mode, however that isn't
> actually the case. All the Strict parameter to 13.2 controls is
> whether or not "poison-pill" properties for 'caller' and 'arguments'
> are created for the function object. The semantics of strict mode
> are specified throughout the ES5 specification and are control by the
> actual lexical occurrence of a use strict directive. The Strict
> parameter to 13.2 does not alter this semantics.
> The HTML5 spec. also contains another related bug. Step three says
> "If the previous steps failed to compile the script, then ..." where
> the "previous steps" pretty clearly references the use of ES5 13.2 in
> the immediately preceding step 2. However, there is nothing in ES5
> 13.2 that concerns the compilation of ECMAScript source text.
> Instead 13.2 expects to be passed an valid FunctionBody. That
> validation ("compilation") must occur somewhere else.
> It appears to me that these problem are probably the result of the
> HTML5 algorithm being patterned after the wrong parts of the ES5
> spec. The appropriate part of the ES5 spec. to use as a model is
> steps 8-11 of ES5 22.214.171.124. This is the definition of the Function
> constructor. These steps correctly take care of parsing the
> FunctionBody and handling any resulting syntax errors. It also calls
> 13.2 with a correct Strict parameter. Replacing HTML5 126.96.36.199 steps
> 2-3 with steps modeled after ES5 188.8.131.52 steps, 8, 9, and 11 (step
> 10 is not applicable) should correct these issues.
> Finally, Kangax also lists as a "non-standard" feature the
> recognition of strict coder as the string argument to setTimeout. I
> couldn't find anything the HTML5 spec. that could be interpreted as
> excluding strict ECMAScript code in this context.
Any chance you could open one or more bugs on this?
Doing it via the bugzilla interface gives you an increased ability to be
notified and participate, but you can also use the form directly on the
W3C spec itself:
Or the form at the bottom of every page on the WHATWG spec:
Whichever way you enter it, it ends up in the same place.
- Sam Ruby
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