On Thu, Sep 17, 2015 at 5:18 PM, Neil <n...@parkwaycc.co.uk> wrote:
> Shu-yu Guo wrote:
>
> 4. The global lexical scope is extensible. This means dynamic scope (lol!):
>>
>> <script>
>> function f() { dump(x); }
>> f(); // prints undefined
>> </script>
>>
>> <script>
>> let x = 42;
>> f(); // prints 42
>> </script>
>>
>> Would you mind clarifying what this is supposed to demonstrate? It looks
> to me that this is demonstrating TDZ semantics, and under ES6 the first
> call to f() will throw.
>
The first call to f() does not throw. These are two separate <script>
tags, and during the execution of the first <script> tag, there is no
global lexical binding named 'x', so no TDZ semantics are triggered.
Instead, undefined is printed because there is no binding named 'x' and
presumably the 'x' property on the global object is undefined.
When we execute the second <script> tag, we now have made a global lexical
binding named 'x'. When we call f() again, it will print the value of that
binding.
To contrast, the following two scripts would throw due to TDZ:
<script>
function f() { dump(x); }
f(); // doesn't throw, prints undefined
</script>
<script>
f(); // throws due to TDZ
let x;
</script>
The second call to f() throws because during the second script's
execution, there is an uninitialized global lexical binding 'x'.
> --
> Warning: May contain traces of nuts.
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--
shu
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