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Looking at a lot of NodeJS and Javascript code recently, it seems arguments is not an instance of Array but still behaves like one, so people do stuff like Array.prototype.slice.call(arguments, ...) or [].slice.call(arguments) which adds verbosity and increases hurdle for newbies to understand etc.. Is there a reason why arguments isnt an instance of Array or is this just one those bad parts?

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NO. arguments is a standalone object that just so happens to have a length property and the ability to use [] to index it. But otherwise, it is just an object, not an Array object.

And yes, this is indeed one of the bad parts of JavaScript.

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Thanks for clarification, I know it has extra properties like .callee etc.. but in an ideal world shouldnt they have pointed the prototype to Array. so it would have splice/slice directly on it. I ask not to shoot the JS developer but only to clarify my understanding, ideally someone will turn around and say my idea is retarded becasue of x/y/z (fundamental misunderstanding etc..) –  user53791 Jan 28 '11 at 7:16
    
@mattcodes Yes, they definitely should have done that. JS has a bunch of quirks, and this is one of them. –  Jacob Relkin Jan 28 '11 at 7:17
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Also don't assign to arguments[0] etc. as arguments[0] is the exact same thing as your first formal parameter, changing either, will also change the other one. –  Ivo Wetzel Jan 28 '11 at 18:30
    
To be explicit, this isn't specific to Node.js. It's in the JavaScript spec. –  frontendbeauty Sep 19 '12 at 20:58
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