Using Object Methods In AddEventListener
Jul 20, 2005
When you use addEventListener (or addEvent in IE) to call an object
method, does it call it with the correct this parameter?
The ECMAScript reference has a lot to say about the caller using
Function.prototype.call or Function.prototype.apply and passing the
correct this pointer for the context, but how does addEventListener
determine the correct this pointer. Or does it just punt and pass the
global context, thus making it impossible to refer to the object this
in an object method used as an event listener?
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Jul 1, 2009
Can assign a new function to a built-in object in Firefox:
But IE and Opera don't have a MouseEvent or HTMLElement that can be set up in the same way. Can you do this in IE or Opera, or just Firefox, and maybe Webkit?
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Mar 20, 2010
I created a method for displaying an object's properties:
As long as renderfunction = false, the object is fine coming out of this function.
However, if I change renderfunction to true, all my properties become undefined. Why isn't this working as I expect it to?
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Mar 25, 2006
I've created an object and within this object, I've added an eventlistener. But the problem now is that after addEventListener is being called to access a callback function, the callback function is not able to access the properties within its own class. Code:
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Sep 8, 2005
I have a javascript function that needs to access methods of a java
object(localTag). In my JSP I'm trying to include hidden fields for
the Strings returned from the getter method calls of the object like
so:
<html:hidden name="FrmCustomerHolding" property='<%=
"localTag.getTagName()" %>' />
<html:hidden name="FrmCustomerHolding" property='<%=
"localTag.getTagValue()" %>' />
If I can do something like this, what is the correct syntax and how do
I access this property in my javascript? When I have a hidden field
that is just a String, I access it in the javascript like
"document.getElementById("theString").value" and it works fine, but I
can't seem to find how to access the String value of a method call.
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Jun 10, 2011
I have more of a programme design related question here: I have an object with 2 methods, those two methods are supposed to be called repeatedly one after the other (e.g. by setInterval())
window.setInterval(function() {
obj.method1();
obj.method2();
}, 100);
the problem with this code is that the execution time of those methods may increase depending on the processed data (an array with several hundred elements or more) so it may be, that the execution time of both methods exceeds the given repetition time. I could solve that by placing a call to the next function in each method, but I wonder if that is good design or not (tight coupling)
code for method2() is analogue
Obj.prototype.method1 = function ()
{
/* working code here */
[Code]....
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Dec 8, 2011
When a custom object is created in javascript, then methods need to be defined for this object. Still every object has toString() method available to them, even if it is not defined. How is this method available to all the objects ? Is it inherited from some root object ?
Is sort() method available to all the objects ? What are the other methiods available to all objects ? Where can I get list of available methods ?
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Jul 23, 2005
I am a little confused how the memory for objects is allocated in
JavaScript. David Flanagan, in "javascript: The Definitive Guide,"
states that each property of a class takes up memory space when
instantiated. So space is created for aMethod three times in this
example: Code:
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May 18, 2011
Let's say I have a Javascript object that looks like this:
{
events: {
"comments:added": this.add,
"comments:removed": this.remove,
"comments:fetched": this.addAll
}
}
I'd like to add this method to it, either manually, using $.extends() or _.extends():
[Code]...
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Jan 17, 2011
Do many programmers remember most of the object properties and methods or do they use IDE or references to find those specific objects. I'm starting to learn Javascript and seeing all the different type of objects available can be depressing. :(
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Aug 18, 2010
i have something like this:
Code:
var o = {
f1:function(a) {
[code]....
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Aug 26, 2009
Code JavaScript:
function dropdown() {
}; dropdown.prototype = {
sele: $('.select'),
city: [],
scope: [],
type: [],
init: function(json) {
if(json.location.length) {
for(var i=0; i<json.location.length; i++) {
this.city[i] = json.location[i].city; .....
this.scope[i] = json.location[i].scope;
}}.....
getUrl: function() {
return location.pathname+location.search;
},
setUrl: function(paramType, param) {
return this.QueryString(paramType) ? this.setQueryString(paramType, param) : this.getUrl()+"&"+paramType+"="+param;
}};
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Jul 23, 2005
Well, I've been working with JS for three years and have a great experience here. But! I still have no really acceptable answer to the following
question:
What is the principle difference between declaring methods/properties
in the constructor function body and via prototypes.
Are there any real GURUs? Let's discuss the issue.
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Apr 13, 2010
I'm attempting to understand the use of privileged methods when used with Object.create. I put together a quick demo (code below) that shows what happens when I use Object.create to create a new object based on one that has a privileged method. The outcome is not pleasant, as changing the value in the first object also changes it in the second. Unless I am reading Crockford's articles incorrectly, this makes Object.create almost useless for anything but objects that have only public members.
I've seen many JavaScript programmers use closures extensively to create private members, and that still holds to be a good programming practice. However I still can't find an elegant way to create inheritance in combination with closures in JavaScript, given downfalls such as the one I mentioned above.With all of that said I still think Crockford has a nice way of programming, creating factory functions that produce objects, staying away from the prototype property and making the language look more functional.
Here's the code to demonstrate what I'm referring to. Firebug needs to be enabled to view the console.debug output, otherwise convert them to alerts.
if (typeof Object.create !== 'function') {
Object.create = function (o) {
function F() {}
[code]....
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Aug 10, 2011
What are the different methods of selecting some of the values in the json object below:
what different selecting methods can you use to get the date, or the views?
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Aug 22, 2010
I have some confusion about the scripts below:
1) is getRule a local variable or global variable, as it has no var keyword, yet it is an inner function of Validation? So without var, I think global, but being an inner function, I think local. So I'm not sure which.
2) In this line of code: var rule = $.Validation.getRule(types[type]), getRule returns rules, which is just a local variable in Validation. I always see that you return functions, but how does returning a local variable that's just an object literal and not a function be able to return true or false? Now the value of rules is an object literal, and this object returns true or false. So we are basically allowed to use return keyword with local variables that are object literals and not functions?
3) In this line, is foo(age) being called, or is it just being assigned to bar OR is it being called and THEN assigned to bar: var bar = foo(age);
4) Now for the most confusing: age is obviously an object reference as opposed to a literal in the example. Does that make a difference in regards to closures?
Note that I read a number of books, including JavaScript Programmer Reference and Object Oriented JavaScript and jQuery cookbook, which compare primitives vs reference types and how primitive types store directly in memory whereas reference tpyes reference memory, so if one reference changes, they all change where primitive remains ingrained. But when assigning a function as a reference like this, how does that affect the object "age" when passed into bar?
Code:
(function($) {
/*Validation Singleton*/
var Validation = function() {
var rules = {
email : {
check: function(value) {
if(value)
return testPattern(value,".+@.+..+");
return true;
}, .....
$.Validation = new Validation();
})(jQuery);
Code:
function foo(x) {
var tmp = 3;
return function (y) {
alert(x + y + tmp);
x.memb = x.memb ? x.memb + 1 : 1;
alert(x.memb);
}}
var age = new Number(2);
var bar = foo(age); // bar is now a closure referencing age.
bar(10);
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Jan 25, 2010
I have an object on the document element that allows for other components to register with it, i have a custom event something along$(document).bind("register",function(thechild)..So in the child object when they are created i call$(document).trigger("register",this);And indeed i get the DOM object. However i'm looking for the plug in object, i want to be able to call methods on the passed childobject and access it's Config.Does that make sense? How can i write a plug in that is applied to various objects that also registers itself with an 'overseer' object on the document element in such a way that i can allow that overseer object to call methods on any registered child objects?
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Sep 21, 2005
This makes my life a bit easier. After executing this script you should be able to addEventListener on all elements instead of determining if you want to call attachEvent or addEventListener.
Edit: This is the original version. The revised version is below
if (!document.addEventListener && document.attachEvent)
{
Object.prototype.addEventListener = function(eventName, func, capture)
{
if (this.attachEvent)
this.attachEvent('on' + eventName, func);
}
var i, l = document.all.length;
for (i = 0; i < l; i++)
document.all[i].addEventListener = Object.prototype.addEventListener;
window.addEventListener = Object.prototype.addEventListener;
document.addEventListener = Object.prototype.addEventListener;
}
Revised version:
This one is harder to use but it is nicer to the DOM and all newly created objects. The problem with it is that addEventListener will only be available after the page loads.
If you want to use addEventListener from a window.onload script make sure that this code is included in the body, not in the head. document.body.onload is called before window.onload.
Now, only elements that already have attachEvent will get an addEventListener. Elements created with document.createElement will automatically get addEventListener.
function createIEaddEventListeners()
{
if (document.addEventListener || !document.attachEvent)
return;
function ieAddEventListener(eventName, handler, capture)
{
if (this.attachEvent)
this.attachEvent('on' + eventName, handler);
}
function attachToAll()
{
var i, l = document.all.length;
for (i = 0; i < l; i++)
if (document.all[i].attachEvent)
document.all[i].addEventListener = ieAddEventListener;
}
var originalCreateElement = document.createElement;
document.createElement = function(tagName)
{
var element = originalCreateElement(tagName);
if (element.attachEvent)
element.addEventListener = ieAddEventListener;
return element;
}
window.addEventListener = ieAddEventListener;
document.addEventListener = ieAddEventListener;
var body = document.body;
if (body)
{
if (body.onload)
{
var originalBodyOnload = body.onload;
body.onload = function()
{
attachToAll();
originalBodyOnload();
};
}
else
body.onload = attachToAll;
}
else
window.addEventListener('load', attachToAll);
}
createIEaddEventListeners();
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Nov 16, 2006
Today I have been testing the event models from Netscape 4.8 and IE 4
to the current crop of browsers. I'd like to write a small event
library similar in purpose to the Yahoo! UI event library but with less
features and code. The Yahoo! event library is one of the best
libraries in YUI but it still seems to me to have some confused
code...that or I'm still confused.
The Yahoo! UI library focuses on using addEventListener and
attachEvent. However, due to the click and dblclick bugs in Safari a
long legacy event workaround is included to use a Netscape4-type event
model for Safari. Something like this
var listeners = [function(event){}, function(event){}];
document.getElementById('blue').onmouseover = function(event) {
for (var i=0; i<listeners.length; i++) {
listeners[i](event);
}
};
With this above example, multiple handler functions can be fired for a
single event. I imagine that this is an old trick that has been around
for a long time, yes?
With all the new browsers I tested with this legacy workaround, the
listener handlers can use event.stopPropogation() or
event.cancelBubble=true and they work as desired. The handler functions
can also use event.preventDefault() and event.returnValue=false and
they too work. These seem to work because the event object passed to
the handlers is a modern event object and not one from Netscape4.
My question is, if Safari needs this legacy workaround, and the legacy
workaround seems to work in all the browsers that have addEventListener
or attachEvent, then why bother with the addEventListener and
attachEvent functions at all? Why not just use the legacy way for all
browsers and all type of events.?
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Apr 19, 2009
I was using this script to learn how to use event listeners and I need to know how to make it work for IE. I keep finding attachEvent scripts that look like they will work, but I get nothing. I've spent several hours finding script after script that simply don't work. I don't know where to turn next. Any script to attach these events to IE?
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "[URL]">
<html>
<head>
<title>Test</title>
</head>
<body><div>
<script type="text/javascript">
if(!Array.prototype.link)
Array.prototype.link = function(f) { for(var Obect1 = new Array(), i = 0, n = this.length, t = arguments[1]; i < n; i++) Obect1[i] = f.call(t, this[i], i, this);return Obect1;};
Array.prototype.linkMethod = function(m) { var n = this.length, args = this.slice.call(arguments, 1);if(typeof m == "string" && n > 0) m = this[0][m];for(var Obect2 = [], i = 0; i < n; i++) Obect2[i] = m.apply(this[i], args);return Obect2;}; .....
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Oct 20, 2006
I'm trying to add a clickevent to an anchor that I created trough DOM.
This his how the code looks:
var oSubLink = document.createElement("A");
oSubLink.appendChild(document.createTextNode("+"));
oCel.appendChild(oSubLink);
oSubLink.addEventListener("click", klapUit(oTabel.id, eigenschappen[2]), false);
It failes at the addEventListener call, saying "No such interface supported" (appears to be one of the two default error messages IE gives when it can't handle your JS :mad: ).
How can I fix this? The solution should work in IE6, FF, Opera, Mozilla and Safari.
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Jul 12, 2007
Is there a way to send parameters to the function being added to an event with addEventListener. I.E. say you have this function
Code:
function someFcn(i){
alert(i);
}
and I add it to an object.
Code:
someElement.addEventListener('focus', someFcn, false);
Is there a way to send a parameter to someFcn.
For Example I have tried this but it failed
Code:
var someString = 'Hello World'
someElement.addEventListener('focus', someFcn(someString), false);
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Sep 9, 2011
I have this code:
for(var h:Number=0; h<4; h++){
var Build : Button;
Build = new Button();
Build.height = 20;
[Code]...
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Jun 1, 2011
Is it possible to add events using addEventListener to multiple radio buttons with same id ?
<input id="radId" type="radio" value="0" name="radioname">No
<input id="radId" type="radio" value="1" name="radioname">Yes
I tried to attach event using document.getelementByID BUT it always picks the first radio button.
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Feb 11, 2007
Task: I would like to implement a CtrlEnter event that would work on both IE and FF.
My approach: use addEventListener() and attachEvent() to capture the event then trigger a function to check for CtrlEnter:
if (oTarea.addEventListener) {
oTarea.addEventListener('keyup', function() {checkCtrlEnter(event);}, false);
}
else if (oTarea.attachEvent) {
oTarea.attachEvent('onkeyup', function() {checkCtrlEnter(event);});
}
function checkCtrlEnter(e) {
if (e.ctrlKey && e.keyCode == 13) {
// do something
}
return false;
}
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Mar 17, 2003
As I understand it so far:
element.attachEvent()
IE 5+ for PC
element.addEventListener()
Gecko, KHTML
element.event
NS3+, IE4+, dunno about opera or others
Since I'm only concerned with attaching a single event and don't care about bubbling/capturing, am I best off not using the old style of event registering to assure maxium compatibility?
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