Someone please correct me if I'm wrong, but JavaScript only has
function scope and global scope. If a variable is not found in the
current scope, JavaScript keeps going up in scopes until it finds that
variable or decides it doesn't exist. This is the case for most
variables, with the exception of `this` and `arguments`, which ALL
functions get. (There may be more, but I dont remember offhand)
Typically `this` can come from an instantiated object that's had a
method called on it, or someone doing a Fn.apply or Fn.call with an
explicit target object. (eg myfunction.apply(myobject, args) => this =
myobject)

Therefore, in order to "hold onto" a previous scope, we just assign it
to `self`. You may a few layers deep in callbacks involving multiple
objects, where it's useful to retain a handle on the top-most object
which you can use in callbacks. Like others have posted here, the name
`self` isn't magical (unlike `this`, which is), you could call it
whatever you want, it's just a convention that's sprung up...

--
Orlando Vazquez