Each time you use one or the other of these methods, the library places a "call wrapper" around your function.  Then, when the new delegate (or callback) is called, there are actually two calls being made: the first to the wrapper, and the second when the wrapper calls your function.

By combining the use of both methods, you're now placing two call wrappers around your function, which is fairly inefficient, not to mention that it's not exactly elegant or readable.

Why would you want to combine the two methods?

You'd want to combine them when you want to ensure that this refers to a specific object, and you also want to pass specific arguments ("context") to the function.

For example, let's start with two objects, each containing an array of messages (strings).   We also have a function that expects that this will refer to one of the objects, and it will expect to receive the index of the message to display as an argument.

(This is a very contrived example, but it shows the requirement and solution in simple terms.  Real-world situations that require the use of both createDelegate and createCallback are more complex.)

var myObject1 = {
    messages: ["Red", "Blue", "Black"]
};

var myObject2 = {
    messages: ["Audi", "Chevy", "Mitsubishi"]
};

function showAlert(index) {
    alert(this.messages[index]);
};

Now, I'll create two delegates/callbacks: one will call....

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