Why does "Javascript the Good Parts" claim that "A property value can be any Javascript value except for undefined"?
<p>As mentioned in the topic JS the Good Parts seems to claim that a property value can't be undefined. However if you do the following in Chrome's console for example:</p>

<pre><code>var foo = {}
foo.bar = undefined
foo
</code></pre>

<p>Then click to expand the foo object you can still see that foo contains a property called bar with the value undefined. Of course from the Javascript side you can't tell the difference between foo.bar returning undefined and foo.unexistingproperty returning undefined. But what is the point of the console still clinging to the property that was set to undefined?</p>
