jQuery Plugin: Adding Callback functionality

Just execute the callback in the plugin:

$.fn.myPlugin = function(options, callback) {
    if (typeof callback == 'function') { // make sure the callback is a function
        callback.call(this); // brings the scope to the callback
    }
};

You can also have the callback in the options object:

$.fn.myPlugin = function() {

    // extend the options from pre-defined values:
    var options = $.extend({
        callback: function() {}
    }, arguments[0] || {});

    // call the callback and apply the scope:
    options.callback.call(this);

};

Use it like this:

$('.elem').myPlugin({
    callback: function() {
        // some action
    }
});

I don't know if I understand your question correctly. But for the second version: This would call anotherFunction immediately.

Basically your plugin should be some kind of function that looks like this:

var myPlugin = function(options, callback) {
    //do something with options here
    //call callback
    if(callback) callback();
} 

You have to provide a function object as callback, so either function(){...} or anotherFunction (without () ).

Bringing back a blast from the past.

Worth noting that if you have two arguments passed, for example:

$.fn.plugin = function(options, callback) { ... };

Then you call the plugin without the options argument but with a callback then you'll run into issues:

$(selector).plugin(function() {...});

I use this to make it a little more flexible:

if($.isFunction(options)) { callback = options }