Question

I would like to use fnB in click handler. Is there any elegant solution? Thanks.

A = function() {
   ...
}

B = function() {
   ...
}
B.prototype = new A();
B.prototype.fnB = function() {}
B.prototype.fn = function() {
  // this isntanceof B -> true
  jQuery(selector).click(function() {
    this.fnB() // this instance of B -> false, this == $(selector) -> true
  }
}

---

Implementation based on SoWeLie’s answer:

EventType = {
    ButtonClicked: 0
    ...
}

function Delegate(object, method) {
    return function() { method.apply(object, arguments); }
}

function Observable() {
    this._eventHandlers = {};
}

Observable.prototype = {
    addListener: function(eventType, listener) {
        if(!this._eventHandlers.eventType) {
            this._eventHandlers.eventType = [];
        }
        this._eventHandlers.eventType.push(listener);
    },

    removeListener: function(eventType, listener) {
        if(this._eventHandlers.eventType) {
            for(var i = this._eventHandlers.eventType.length; --i > -1;) {
                if(!listener || this._eventHandlers.eventType[i] == listener) {
                    this._eventHandlers.eventType.splice(i, 1);
                }
            }
        }
    },

    fireEvent: function(eventType, data) {
        if(this._eventHandlers.eventType) {
            for(var i = 0; i < this._eventHandlers.eventType.length; ++i) {
                var handleEvent = this._eventHandlers.eventType[i];
                if(handleEvent) {
                    handleEvent(this, data);
                }
            }
        }
    }
}

Dialog.Buttons = { ButtonOk: 0, ButtonCancel: 1, ButtonYes: 2, ButtonNo: 3, ButtonClose: 4 };
Dialog.prototype = new Observable();
Dialog.prototype.bindEvents = function() {
    $('#dlgButtonOk', this._$el).click(Delegate(this, function() {
        this.fireEvent(EventType.ButtonClicked, Dialog.Buttons.ButtonOk );
    }));
    $('#dlgButtonCancel', this._$el).click(this, function() {
        this.fireEvent(EventType.ButtonClicked, Dialog.Buttons.ButtonCancel );
    });

$(function() {
    dialog = new Dialog('.dialogWnd')
    dialog.addListener(EventType.ButtonClicked, function() {alert(1)})
});

????
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Your post does not have much context to explain the code sections; please explain your scenario more clearly.
???

Answer 1

The most elegant solution is to use the apply method of a function:

var hitch = function (scope, callback) {
        return function () {
            return callback.apply(scope, Array.prototype.slice.call(arguments));
        }
    }

Change your code like so:

jQuery(selector).click(hitch(this, function() {
    this.fnB() // this instance of B -> false, this == $(selector) -> true
  }))

Notice the call to hitch on your anonymous function, this will ensure the cope is preserved within the click handler.