Behavior of Object.bindProperties() Method of Nashorn

[A. Sundararajan]

Object.bindProperties considers properties at the time of bindings only. 
No "tracking" of object after it is bound. Also, only properties that 
don't exist in target object are bound from source (again check is at 
the time of binding).

Hope this helps,
-Sundar

On Friday 10 October 2014 11:08 PM, Kishori Sharan wrote:
> Hello Everyone,
>
> I was experimenting with the Object.bindProperties() method in Nashorn and
> found a few weird behaviors. I would like to ask two questions:
> 1. Is there a comprehensive documentation for this method, except at
> https://wiki.openjdk.java.net/display/Nashorn/Nashorn+extensions#Nashornextensions-loadWithNewGlobal
> 2. Is it a bug as explained in the following snippet of code?
>
> The following code does not bind the x, y, and z properties of obj2 to obj
> because obj already has properties with the same names. Is it documented
> somewhere?
>
> var obj = {x:10, y:20, z:30};
>
> var obj2 = {x:100, y:200, z:300};
>
>
>
> // bind properties of 'obj2' to 'obj'
>
> Object.bindProperties(obj, obj2);
>
>
>
> print(obj.x, obj.y, obj.z);
>
> print(obj2.x, obj2.y, obj2.z);
>
> ---------------------------------
>
> 10 20 30
>
> 100 200 300
>
> --------------------------------
>
> Now, let us add a new property to obj2. The new property is bound to obj,
> but obj reads the new property's value as null:
>
> var obj = {x:10, y:20, z:30};
>
> var obj2 = {x:100, y:200, z:300};
>
>
>
> // Add a new property to obj2
>
> obj2.u = 600;
>
>
>
> // bind properties of 'obj2' to 'obj'
>
> Object.bindProperties(obj, obj2);
>
>
>
> print(obj.x, obj.y, obj.z, obj.u);  // obj.u is null. Why?
>
> print(obj2.x, obj2.y, obj2.z, obj2.u);
>
>
>
> ---------------------------------
>
> 10 20 30 null
>
> 100 200 300 600
>
> --------------------------------
>
> And, here is another variant of the code that works. This time, I started
> the target object as empty. Now, adding the new property to the source
> works fine.
>
> var obj = {};
>
> var obj2 = {x:100, y:200, z:300};
>
>
>
> // Add a new property to obj2
>
> obj2.u = 600;
>
>
>
> // bind properties of 'obj2' to 'obj'
>
> Object.bindProperties(obj, obj2);
>
>
>
> print(obj.x, obj.y, obj.z, obj.u);  // obj.u is correct.It is 600
>
> print(obj2.x, obj2.y, obj2.z, obj2.u);
>
>
>
> ----------------------------
>
> 100 200 300 600
>
> 100 200 300 600
>
> ----------------------------
>
> I am using JDK version 1.8.0_20.
> Thanks
> Kishori