What is the correct output (meaning correct by the ECMA standard) of the following program?
function nl(x) { document.write(x + '<br>'); } nl(Function.prototype); nl(Function.prototype.prototype); nl(Function.prototype.prototype == Object.prototype); nl(Function.prototype.prototype.prototype); Chrome and IE6 agree in saying:
function Empty() {} null for Chrome / undefined for IE6 false and then crashing.
Mozilla outputs:
function () { } [object Object] false undefined Are either of these correct? It seems that the Mozilla one does better, but that the best output is
function () { } [object Object] true undefined
What you’re doing here isn’t really walking the prototype chain – this question might help you understand what is actually going on. I didn’t bother to check the ECMA spec, but here is my take on the issue:
Function is the constructor of function objects
Function.prototype is the prototype from which all function objects inherit – it might contain properties like call and apply which are common to all Function instances; the implementations you checked were consistent in that it is implemented as a function object itself (as some pointed out, the ECMA specification requires this)
Function.prototype.prototype does’t really make much sense, but as Function.prototype is implemented as a function object (which could possibly be used as a constructor), it should at least exists; objects which are created using Function.prototype as constructor would inherit its properties – but as there should be no reason to do something insane like this, setting it to null, undefined or an empty object is reasonable
Function.prototype.prototype.prototype will in all likelyhood be undefined: as we have seen before, Function.prototype.prototype should be something without properties (null, undefined or an empty object) and definetely not a function object; therefore, its prototype property should be undefined or might even throw an error when trying to be accessed
Hope this helps 😉