Bind is transient
=================


Test code
---------

Here's the test code for attribute bind.

.. literalinclude:: /core-javascript-work/tutorial.js
   :language: javascript
   :start-after: start transient-bind
   :end-before: end transient-bind


Discussion
----------

We create an object that has a *return_this* method.  The outcome of
calling *return_this* depends on how it is called.

There's a logic in the test code that produces contradictory, or at
least surprising, outcomes.

From

.. code-block: javascript

   obj.return_this === return_this;
   method_deferred === obj.return_this;
   method_deferred === return_this;

we would expect

.. code-block: javascript

   obj.return_this() === return_this();
   method_deferred() === obj.return_this();
   method_deferred() === return_this();

But this means that in *obj.return_this()* the *obj* is not relevant.
But JavaScript (or its designers) wanted objects to have methods, so
they introduced a special rule.


Explanation
-----------

JavaScript does not distinguish classes and instances.  Python, and
perhaps other dynamic languages, does.  This allows Python to supply a
bound method, which retains a reference to the object, when a function
belonging to the class is called on an instance.

Here's a Python (version 3) command line dialogue that illustrates
this.

>>> def method(): pass          # The function.
...
>>> class A: method = method    # The class.
>>> A.method                    # Function from class.
<function method at 0x15be518>
>>> A.method is method          # Same as the original function.
True
>>> a = A()                     # Instance.
>>> a.method                    # Bound method, not original function.
<bound method A.method of <__main__.A object at 0x16b9d10>>

The odd behaviour shown in the JavaScript test code is a consequence
of JavaScript not distinguishing between classes and instances.