scope_example.js

// This function returns a new function that will run
// the given function in the context of the given scope
// ie 'this' will be whatever you pass in as 'scope'
function scoped(fn, scope) {
  return function () {
    return fn.apply(scope, arguments);
  }
}

var Obj = {
  test: 'success',
  a: function() {
    console.log(this.test);
  }
};

// This works as expected -- the 'a' function is run with
// 'this' being Obj by default.
Obj.a(); //=> 'success'

// We can use the Obj.a function as a callback function
// for this jQuery click event. It seems like it should work fine...
$('#el').click(Obj.a);

// ...but it doesn't. jQuery runs event callback functions in
// a scope where 'this' is the clicked element. Usually this is
// helpful, but in cases like this, we will get an error.
$('#el').click(); //=> Error -- $('#el') doesn't have a 'test' property

// To fix this problem, we need to use the scoped function to
// explicitly run the Obj.a function in the context of Obj.
// Now 'this' will be Obj rather than the clicked element.
$('#el').click(scoped(Obj.a, Obj));
$('#el').click(); //=> 'success'