Can't Apply Object.defineproperty To An Array.length

[graduate]

Hello, It is my first message on this forum and I'm currently learning JavaScript. When I try this code

var a = [1,2,3];Object.defineProperty(a, 'length', {value:10, writable:false});

I get an error from Firebug - "defining the length property on an array is not currently supported". I've read in the fresh 6th edition of "Java Script" book of David Flanagan that I can make a length property of an array unwritable with Object.defineProperty method, but I get the same error from Firebug when I try to apply this method a to change any property (value, writable etc.).

[Ingolme]

You can't modify the length property of an array. It doesn't make logical sense. If an array has 5 elements and you set the length to 3, you've messed up the whole structure.

[graduate]

No, I can change the length property of an array, but I can't apply Object.defineProperty to it.

[Ingolme]

Hmm, the length property is writeable...If Firefox tells you it's not supported yet, then there really isn't anything you can do about it.