If I try this using standard Javascript instead of __defineGetter__, I get
a more descriptive error when it fails (in Node only):
> Object.defineProperty(f, 'length', { get: function() { return 5; } });
TypeError: Cannot redefine property: length
And digging deeper:
> Object.getOwnPropertyDescriptor(f, 'length')
{ value: 3,
writable: false,
enumerable: false,
configurable: false }
Looks like the version of V8 Node is using defines length as a
non-configurable property. In Chrome the same function says "configurable:
true", so that behavior must have changed.
That being said, anything I've ever used which used the length of a
function always causes headaches... various function composition functions,
such as .bind will, depending on the version of V8 or Javascript engine (or
other 3rd party modules which polyfill over the standard .bind) will often
return a misleading result (on older versions of V8, and most
polyfills, (function(a,b) {}).bind().length would be 0 instead of 2, since
the return function isn't declared with any parameters).
Jimb Esser
On Sunday, July 19, 2015 at 1:56:05 PM UTC-7, Robert Steckroth wrote:
>
> I need to override the length property of the Function constructor for a
> wrapper I am making. Why does the following code work in Gecko and Mazilla
> browsers but not nodejs?
>
> var f = function(a,b,c) {}
> f.length // = 3 <- length is three because 3 parameters are expected by
> the function
>
> f.__defineGetter__("length", function() { return 5 })
> f.length // = 5 <- length is now five because f __proto__.length has been
> overwritten with a property
>
> The above code works in the latest Chrome and Firefox but not in Nodejs, i
> wonder why..
>
>
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