How to make an assignment reference the left operand

[csdude55]

This is really just for fun, and my own education.

Let's say that I have this:

str = func(str);

function func(oldStr) {
 // do stuff
 return newStr;
}

Is there a way to modify func() so that, if oldStr is not explicitly defined, it would use the value of str (the left operand of the assignment)?

I know that I could do this, of course:

function func(oldStr = str)

but in production I wouldn't know the name of the variable that was assigned. So I'm trying to figure out if there's a built-in variable that equals the value of the left hand operator.

The end goal is to be able to use str = func(); without typing str twice :-)

[Fotiman]

The short answer is no, there's no built-in variable that equals the value of the left hand operator.