howto install event handler

[nstasiv@gmail.com]

Hello,
the idea is to make object draggable with code like this

var callout = new Callout(...);
new Draggable(callo ut);
where new Callout(...) adds some elements to DOM tree and new Draggale
does the trick:

function Draggable(_obj) {
this.obj = _obj;
this.clickedX=0 ;
this.clickedY=0 ;
this.origX=0;
this.origY=0;
this.obj.onmous edown = function(evt){
this.pickup(evt );
}
this.obj.onmous eup = function(evt){
this.dropoff(ev t);
}
this.obj.onmous emove = function(evt){
this.givealift( evt);
}
}

Draggable.proto type.givealift = function(evt).. .
Draggable.proto type.pickup = function(evt).. .
Draggable.proto type.dropdown = function(evt).. .

I used to install event handler with e.setAttribute( "onmousedow n",
"pickup(evt )")
and everything worked fine, then I made scripts in object oriented way
but code
this.obj.onmous edown = function(evt){
this.pickup(evt );
}
won't work as expected, please help!

Thank you
Nazar

[Richard Cornford]

Re: howto install event handler

nstasiv@gmail.c om wrote:
<snip>

this.obj.onmous edown = function(evt){
this.pickup(evt );
}
won't work as expected, please help!

In javascript the value of - this - is determined entirely by how a
function is called and has no relationship with how or where code that
uses it is declared/defined. When the browser calls an event handler
assigned to an event handling property of an Element it calls that
handler as a method of the Element, and so - this - is a reference to
the Element.

There are several techniques for associating DOM Element's event
handlers with javascript object instances. Many are based upon
closures:-

<URL: http://jibbering.com/faq/faq_notes/closures.html >

Richard.

[nstasiv@gmail.com]

Re: howto install event handler

As I understand code

this.ctl.getObj ect().addEventL istener("moused own",
function(evt){t his.pickup(evt) ;}, false);

has the problem where this.pickup(evt ); is called. Am I right?

If there is no easy way to do the trick I will dig into closures
subject. Thank you for help!

Richard Cornford wrote:

nstasiv@gmail.c om wrote:
<snip>

this.obj.onmous edown = function(evt){
this.pickup(evt );
}
won't work as expected, please help!

>
In javascript the value of - this - is determined entirely by how a
function is called and has no relationship with how or where code that
uses it is declared/defined. When the browser calls an event handler
assigned to an event handling property of an Element it calls that
handler as a method of the Element, and so - this - is a reference to
the Element.
>
There are several techniques for associating DOM Element's event
handlers with javascript object instances. Many are based upon
closures:-
>
<URL: http://jibbering.com/faq/faq_notes/closures.html >
>
Richard.