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Thread: how to listen a function?

  1. #1
    Join Date
    Jan 2008
    Posts
    22

    Angry how to listen a function?

    I have created two functions aa and bb. now I hope, when I call aa, the bb will be also invoked. How to do that? I mean, don't write the bb invoked code in aa. I hope just like "dojo.connect(a,"aa",b,"bb');", I don't know how does the dojo realize it.

  2. #2
    Join Date
    Oct 2006
    Location
    Ontario Canada
    Posts
    1,160
    would something like below work?

    Code:
    function connect(function1, function2)
    {
    	eval(function1)();
    	eval(function2)();
    }
    
    function aa()
    {
    	alert('I am aa function');
    }
    
    
    function bb()
    {
    	alert('I am bb function');
    }
    
    //TEST IT ALL
    connect('aa','bb');
    Drew

  3. #3
    Join Date
    May 2003
    Location
    Between Baltimore and DC
    Posts
    3,579
    Another idea to play with:

    Code:
    function foo(fnc){
     fnc();
    }
    
    function bar(){
      alert("bar");
    }
    
    foo(bar);
    Eric
    Tech Author [Ajax In Action, JavaScript: Visual Blueprint] | twitter | linkedin | http://www.pascarello.com

  4. #4
    Join Date
    Jan 2008
    Posts
    22
    Thanks for your response. I'm sorry. recently, I am learning the dojotoolkit. maybe, I didn't describe the question clearly.
    This is the test code I used in my page with dojotoolkit:
    <script src="dojo.js"></script>
    <script>
    function ab(){
    this.a = function(){alert("b");}
    }
    function ac(){
    this.a = function(){alert("c");}
    }
    var b = new ab();
    var c = new ac();
    dojo.connect(b,"a",c,"a"); // here use c.a to listen b.a
    b.a(); //b.a is called, and c.a is also invoked
    </script>

    As above, I call b.a, but c.a is also invoked, I don't know how does it work?
    in the ab.a, I don't write any code to invoke the ac.a, but it do, why?
    I mean how does the dojo connect these two functions.
    I guess the dojotoolkit modify my b.a function, and add some codes to call the c.a, but I can't find out it.
    I have read the source codes of dojo, but didn't find any clue.
    Is there anyone familiar with dojotoolkit?
    give me some clues, please!
    thank you!

  5. #5
    Join Date
    Aug 2007
    Location
    Somewhere in the vicinity of Betelgeuse
    Posts
    194
    While I'm not sure what the dojo implementation looks like, here's a quick one I hacked together (this type of thing is part of something called Aspect Oriented Programming, hence the name of the object).
    PHP Code:
        Aspect = {
            
    after: function(abcd) {
                var 
    ab a[b];
                
    a[b] = function() {
                    
    ab.apply(aarguments);
                    
    c[d].apply(carguments);
                }
            }
        }; 
    So, when you call Aspect.after(...) it creates a copy of the original function and then replaces it with a function which first calls the copy and then calls the "listening" function, both with the same arguments, and both in the context of their object.

    I have put a quick sample here: Aspect.

    You can read about the apply function here.
    Not one shred of evidence supports the notion that life is serious.
    eternal.co.za - code, thoughts, rants and raves
    f1rivals.net - formula 1 forums, and, hopefully, soon, prediction game

  6. #6
    Join Date
    Jan 2008
    Posts
    22
    Great! This is just what I need.
    Thank you,Mr Moo, and two brothers above, you do me a big favor!

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