Property descriptor object of length property shows configurable: true, writable:true and enymerable:true but it behaves like read only.

I knew that readonly feature can only be implemented by PDO(property descriptor object).

Can someone give any clue?
How is this readonly?

```
var nodeList = document.getElementsByName('demo');

nodeList.length; //3
nodeList.length = 6;
nodeList.length; //3

Object.getOwnPropertyDescriptor(nodeList,'length')
Object
configurable: true
enumerable: true
value: 3
writable: true
__proto__: Object

```