On Mon, 22 Dec 2014 21:06:18 +0800, Glen Huang <[email protected]> 
wrote:>Ideally it shouldn’t, because its twin `for (var a in null) {}` won’t.
>
>But looking at step 8 in 
>https://people.mozilla.org/~jorendorff/es6-draft.html#sec-runtime-semantics-forin-div-ofexpressionevaluation-abstract-operation,
> when passing `null` to `GetIterator()`, it will throw a type error when the 
>result of step 2 `CheckIterable(null)`, which is `undefind`, is called in step 
>3 in the algorithm for `GetIterator()`.>
>Did I miss something or the current spec does throw an error?

To me since `IsCallable(undefined)` is `false`, so it throws an `TypeError`. 
Traceur and V8 will both throw a `TypeError` saying that cannot read property 
@@iterator from undefined or null, and Firefox throws a `TypeError` saying that 
null have no property. So it should be an error.                                
       
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