What's the difference between window.x and x?
<p>Let's say, "x" is a variable that never defined, so it should be undefined. In the following scenario:<br>
1)</p>

<pre><code>if(x){//do something}
//ReferenceError: x is not defined
</code></pre>

<p>2)</p>

<pre><code>if(window.x){//do something}
//worked as expected
</code></pre>

<p>As far as I know, in browser environment here, x should be the same as window.x, could anyone help to point out the reason for the different behavior here?</p>
