When you assign a DOM element an ID, that ID becomes part of the window object. No joke, in the spec even ( emphasis mine ):
7.2.4 Named access on the Window object
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The Window interface supports named properties. The supported property names at any moment consist of the following, in tree order, ignoring later duplicates:
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the value of the id content attribute of any HTML element in the active document with a non-empty id content attribute.
On josephscott.org the sidebar section has an ID of “sidebar”, which is easily accessed in the Chrome Console:
I’d recommend never doing this in real code ( great for quick debugging in the JavaScript console though ). Instead stick with document.getElementById( 'thingid' );, which is significantly faster.