So when you're dealing with objects and classes,
you might need to interrogate the members of those classes.
And JavaScript supports this in a fairly simple way.
If we look at some objects that we've created or this could be class, we can simply use the
FOR in syntax to iterate through the property names of the object that you're looking at.
So here we can pop up and alert and this will show us the property name
that is defined in the customer.
And this will show us for each property name.
To get the value we then can just use the bracket syntax we saw earlier just pass
in the property name to get back the value.
This value maybe a function, maybe strings, numbers, any sorts of data.
You'll have to use the type of operator to determine what the property type is
so you can do the correct thing with it.
In addition, you can detect those properties by calling hasOwnProperty.
This will allow you to take an object, test for a property name, and this return a Boolean
with whether this object you've called it on has that property name.
You can also test whether a property is enumerable as well.
These are traditional way that when you're calling into a function that requires
that interface to make sure the object passed in has the correct property names that you need.