javascript function pointer and "this"

Question

Using jsPlumb to bind, I'm passing a method as a variable to be used as a callback. When its called, the "this" is not the object the method is a member of. How do I go about getting access to the method's object instance so I can get access to it variables and other member functions?

I have no control over the callback call method, its a separate library. All I do is call the binding from my object init method. I would have expected this inside my _connection method to have been its object.

jsPlumb.bind('connection', this._connection);

Answer 1

The value of this for any function is determined when it's called. The function really has no other ties to the "object" than whether or not it was called as object.method() or method.call(object).

So, to pass a function with a fixed this value, it'll need to be bound:

jsPlumb.bind('connection', this._connection.bind(this));

jQuery also includes a wrapper and compatibility fill for this with jQuery.proxy():

jsPlumb.bind('connection', $.proxy(this._connection, this));