I'm writing a base class for a project and one of the class's prototypes encapsulates cross browser event listening. One point of confusion is that removeEventListener requires that you know the handler. I don't have this info because I'm creating anonymous functions, so how do I do it?Here's the code:
javascript Code:
Original
- javascript Code
[code]....
Background: I have a menu which is created from an AJAX response - a php Do While loop whose size depends on the database content. Each click leads to a new sub-query. (The user gradually opens up all the options from header, to sub-header, to category.)
When you get to the category level, the click event fills a new div with thumbnail images, which you click to get product details. There is also a mouseover event on the category on the menu (not the thumbnail) which shows a few small images elsewhere on the page. However, I need to disable this mouseover event after the click. BUT... each category has a (unique) id generated by a combination of a static name category concatenated with a unique id taken from a database, (eg category1541, category1542 etc,) which is used to identify the product details correctly and bring up the correct images.
So here's the problem. After I have made the click event, I want to disable the mouseover event on all the category elements, not just the one I clicked.
Here's the function for FF browsers. (I will do the same later using DetachEvent later for IE.) I started using getElelmentByID, which didn't do what I wanted, so I changed to the window element.
If it is relevant, tinythumbs(this) is unique to the category.
I know this is complicated so I could post more code, but it's pretty big and full of php and the js file is referenced.
There exists anonymous function, and you could also use a variable to contain such function. But why no class?
I mean, you could do:
$func = create_function('$a', 'print $a;');
$func();
or
function test($a)
{
print $a;
}
$func = 'test'
call_user_func($func, xx);
But there is no:
$class = create_class('', '');
or
$class = 'MyClass'
class $class {}
Why?
Is it possible to iterate through an anonymous array of strings with a for loop?
Here's what I'm trying to do:
for ( i in ['country', 'city', 'state'] ) {
doSomethingWithString(i);
}
What I want is the string, but what I'm getting is the index number of the array, which I can't use because the array isn't named.
I'm not having any luck writing this:
Code:
<a onclick="function(e) {clicked(e, 1);}">hit me</a>
and don't have the option of defining the click event outside the <a> tag.
Is it possible to pass in the click event and an additional parameter to the clicked function?
I have a problem with understanding jQuery. In my case I have this JS file with following content (see below). This is an anonymous function, isn't it? The problem is this line:
[Code]...
I have been struggling with a form wizard all day. I'm using jquery stepy (form wizard) along with validation plugin. To cut a long story short, my first step is to get MySQL connection from form controls details. On submit ('next' button) a check is made on an empty hidden control ('hid').
rules: {
hid: {
required: function(){
return checkDBData();
},
messages: {
hid:
{required: 'SQL not available'},
...(etc)...
So, if the function checkDBData passes, false should be returned, so that the form can progress to the next step. If the connection details fail, true is returned so that an error msg is posted.
Here's the checkDBData function:
function checkDBData(){
var host = $('#mysql_host').val();
var username = $('#username').val();
var password = $('#password').val();
var dbname = $('#dbname').val();
$.post("install/sqlcheck.php",
{"host": host,"username": username, "password": password, "dbname": dbname},
function(msg){
if(msg.required == false){
return false;
}else{
return true;
}},
"json"
);
}
The return values don't find their way back to the rules. However, if I hard code false and true to the function...
function checkDBData(){
var host = $('#mysql_host').val();
var username = $('#username').val();
var password = $('#password').val();
var dbname = $('#dbname').val();
$.post("install/sqlcheck.php",
{"host": host,"username": username, "password": password, "dbname": dbname},
function(msg){
if(msg.required == false){
return false;
}else{
return true;
}},
"json"
);
return false; //or return true for testing purposes
}
This works. I assume it's due to the asynchronous nature of the ajax call.
I'm having trouble with something that I can't explain outside of an example. Code:
Code:
$js_info_tabs = json_encode($valid_array);
$script = <<<JAVASCRIPT
<script type="text/javascript">//<![CDATA[
function changeTo(id) {
[Code]....
I have the code this way in order to consolidate it since I would prefer to do that instead of checking the selected ID and manually checking against all possible IDs (which works flawlessly, it just takes up about 5x the lines and is not modular). What I have above also works, but there is one fatal flaw:
It seems like the anonymous function that is the onclick for each unselected element becomes "return changeTo(tab + '_id')", but I don't want it to be that. I want the argument to actually be what tab is instead of the variable.
What ends up happening is that after changeTo() is called for the first time, any element you click will result in the last element being the selected one, as if it's using the final value of tab as its return value.
This doesn't make any sense, though, since tab is local, and deleting it before the function exists doesn't work. Deleting elem at the end of the for loop doesn't work. I honestly don't understand what's going on or why it doesn't set the new onclick value correctly.
Basically I just want changeTo(tab + '_id'); to turn into changeTo('MYID_id'); instead, but it simply doesn't do that and I can't figure out a way how.
var name = "good";
load_image( name );
function load_image( name )
[code]....
I've tried giving addEventListerner an anonymous function
I have several functions with code along the lines of:
var xmlDoc = requestXML("ajax.asp?SP=SelectRelatedTags&tag=" +
array[i]);
The requestXML() function includes the code:
var xmlDoc = null;
http_request.onreadystatechange = function() {
if (http_request.readyState == 4) {
if (http_request.status == 200) {
xmlDoc = http_request.responseXML;
} else {
alert('There was a problem with the request.' +
http_request.status);
}}};
http_request.open('GET', url, true);
http_request.send(null);
return xmlDoc;
However, the last line (the return) executes before the readyState
reaches 4. How do I return the xmlDoc to the functions only once the
xmlDoc has been assigned? I tried putting the return statement in a
while loop with the condition that the readyState must = 4 - this
worked, but makes the browser popup a message saying the script is
slowing down the system.
I did search the forums but couldn't seem to find anything on this specifically. I basically need to pass a key event and a 'name' to nameCheck() after 3 seconds. This works fine in Firefox but Internet Explorer gives the error: Member not found. I'm more of a PHP guy than a JS one
<input type="text" onkeyup="nameCheckTimer(this.value, event)" value="" />
function nameCheckTimer(name, evt) {
setTimeout(function(){return nameCheck(name,evt)}, 3000);
}
function nameCheck(name, evt) {
//need name and the key event to be available here. I have code to handle the key codes which works fine
}
I'm working with nested functions and trying to pass a 'this' value to an anonymous being used in an assignment for an event listener.So, this should plop a button inside our DIV and when clicked I'd like it to run the alert-ding; unfortunately it seems to want to run the function as defined under the buttons object which doesn't work out too well.
View 3 Replies View RelatedNormally, if you want to bind encapsulated event listeners to an object you have to test for support and then call the same function in different ways, for example:
if(typeof document.addEventListener != 'undefined')
{
document.addEventListener('click', someFunction, false);
}
else if(document.attachEvent != 'undefined')
{
document.attachEvent('onclick', someFunction);
}
But there's code repetition there - okay not very much, because it's just a function call ... but what if you wanted to use an anonymous function ..? Well you can't - the code repetition would be unacceptible.
Except that I've though of a way :) It's really obvious actually .. but I'm posting this in the hope that others will go "wow, that's blindingly useful" as I did when I thought of it :thumbsup:
Here it is - it takes advantage of square-bracket notation to use a string reference to the supported method:
//identify supported method of adding encapsulated event listeners
etype = (typeof document.addEventListener != 'undefined') ? 'addEventListener' : (typeof document.attachEvent != 'undefined') ? 'attachEvent' : 'none'
//set event name prefix
eprefix = (etype == 'attachEvent' ? 'on' : '');
//if encapsulated event listening is not supported, don't continue
if(etype == 'none') { return; }
so anonymous functions are built like this:
element[etype](eprefix + 'event', function()
{
... code ...
}, false);
Even though attachEvent doesn't require a third argument, it's ignored, so this syntax works for all.
I would like to know how to pass in a reference of this to anonymous function so I can access parameters from anonymous. Here is my code:
[Code]...
I think the last thing people seem to learn about in JavaScript when they're not coming from other programming languages is variable scope. Some even get all the way into AJAX without having learned about scope, and this is a time when it's really needed. Although the scope of JavaScript variables is non-complex by nature, it's something we should all get a full understanding for before we move too far.
Section 1: What is "scope"?
Section 2: The "var" keyword
Section 3: The "this" keyword
Section 4: Closures or "Anonymous functions and self-invoking closures
I am confused about the true difference between the two below examples.
first example:
// Demonstrating a problem with closures and loops
var myArray = [“Apple”, “Car”, “Tree”, “Castle”];
var closureArray = new Array();
[code]....
Here we iterate through the length of myArray, assigning the current index of myArray to theItem variable. We declare closureArray 4 times as an anonymous function. The anonymous function in turn declares the predefined write() function, which is passed parameters. Since write() is in closureArray() a closure is created??? During each iteration, theItem is reassigned its value. The four closures reference this value. Since they reference this same value and since this value is reassigned ultimately to the value of the fourth index position, tHe time we execute closureArray later on, all four closures output the same string. This is because all four closures are within the same scope "the same environment" and therefore are referencing the same local variable, which has changed.
I have a couple of problems with this example:
1) I thought a closure is a function that is returned - the inner function is not returned above.
2) theItem is not even a local variable of the parent function (closureArray) - I thought in order for a closure to work, the inner function only accesses the local variables of the outer function, but in this case the local variable is defined OUTSIDE of the parent function.
3) the "the four closures are sharing the same environment." The thing is even in the second example, they are sharing the same environment.
Second example:
// A correct use of closures within loops
var myArray = [“Apple”, “Car”, “Tree”, “Castle”];
var closureArray = new Array();
[code]....
Here we iterate over the length of myArray (4 times), assigning the index of myArray to theItem variable. We also return a function reference to the closureArray during each iteration (closureArray[i]), where i is index number so we assign 4 functon references. So when we iterate through myArray, we immediatelly call the writeItem() fucntion passing an argument of theItem at its current value. This returns a child anonymous function and when that child function is called, it will execute a block that calls the predefined write() method. We assign that returned anonymous function to the variable closureArray. Hence, closureArray holds a reference to that anonymous function. So closureArray during each iteration holds a reference to the anonymous function and we later call closureArray, which in turn calls the anonymous function, therefore calling the predefined write() function to output the local variable of the parent function. This outputs each distinct index of myArray.
This is because since we created the closure, when we call writeItem, passing theItem argument, since theItem is a local variable of the parent function of the closure, it is never destroyed when we later call closureArray (the reference to the child anonymous function)? Yet weren't we using a closure in the first example as well? So whey wasn't those variables preserved?
I don't think it has anything to do with assigning a returned anonymous function to closureArray. Even though an anonymous function creates a new memory position in the javascript engine, therefore not overwriting the other function references we create during the iteration, it's still referring to a local variable declared outside the reference. So if it's about the closure retaining value of parent's local variable even after exiting the parent function allowing for the current indexes to be preserved, then why did the closure in the first example fail to retain each index?
I am trying to create an anonymous function for onchange event of file field, so that when a file is selected, the covering text field gets that value. I know how to accomplish this by adding onchange="", but I'd prefer not do that. The code that I have almost works, except that the function in the for loop can't call on the "i" variable that the loop uses.
for( i = 0; i < source.length; i++) {
source[i].onchange = function() {
name[i].value = this.value;
}
}
//<input type="text" id="s_field" value=""/>
var valid = true;
var div = $("#s_field");
$.post("index.php",{id: 6}, function (data){
[Code]..
When posting data, and getting response need to set valid to false - email is not valid.
1. in function it alerts valid is false
2. outside function it says valid is still true!
even i didn't wrote var valid = false;, but valid = false;I need to set Global "valid" variable to false.
I'm using jquery to make it easy for AJAX calls.
So I create a class: function cMap(mapID){//vars and stuff}
I go and prototype a function: cMap.prototype.loadMap = function(){ //jquery AJAX call }
Now in the jquery $.ajax({...}); call, I use an anonymous function on the "success:" call: success: function(data){ this.member = data; }
My problem is that inside this anonymous function call I'm trying to call a class member of my cMap class to store the data in from the AJAX call, but it's out of scope. So the JS console in FF/Chrome throws errors about bad value/doesn't exist.
How can I access this class member from inside an anonymous function? Or at least what's a good way to go about doing all this?
I have the following code. This code is working fine in FF but not in IE.
View 3 Replies View RelatedI'm seeing surprising behavior, consistent across Opera, Firefox, and IE.
An event handler is changing the value of an element, and there is apparently
no Change event being generated for the element. A simple illustration is,
make an INPUT element with an onchange; type in a new value, the Change
event handler is called. But make a button whose Click handler changes the
value, and the Change handler does not get called.
It appears that events are not generated while an event handler is running.
Can this be true?
How can I interrupt the enter key so it won't trigger unwanted events on my
web page? I have tried this:
var defaultEventHandler = obj.getEvent("onkeydown");
var myEventHandler = function(event){
if(event.keyCode==13){
alert(obj.getProperty("selection/index"));
}
else{
defaultEventHandler.call(this, event);
}
}
obj.setEvent("onkeydown", myEventHandler);
But it won't even enter the function.
I am trying to handle my mouse movements myself in my JavaScript
application which is ok except for the following problem.
If I happen to click on an image and then move the mouse, the "no-drop"
icon appears as the browser is starting to drage the image url
somewhere. When this happens, I no longer recieve any mouse events in
my JS app. This can be prevented in IE by adding an event handler for
the onDrag event that simply returns false. This prevents IE from
continuing to try and drag the image and instead it continues to send
mouse events.
However, I cannot find a way to do this in Firefox. Can anyone help?
When using variables in click handlers, is there a way to use the value of the variable when the handler was setinstead of run? For example:
var links = new Array;
for (i = 0; i < 5; i++) {
links[i] = document.createElement('span');
$("body").append(links[i]);
[Code]....
All five of the "Click here!" create an alert with the number 5, which was the last value iwas. How can I have each click function use the value of iwhen it was looping through (0, 1, 2, 3, 4)?
I have simplified the problem - see image.[URL]I instantiate object obj1 which inturn instantiates subObj1. subObj1 is a slave to obj1. obj1 registers a handler function called method1 with subObj1 so that subObj1 can tell obj1 when it has finished.For example: call subObj1.subMethod2() to get the sub object to do something.subObj1 calls subMethod1 when its finished with its task, which inturn causes method1 to be called.
If I call method1 directly from obj1 'this' refers to obj1.However when method1 gets called by the subObj1 through the event handler mechanism,I find that 'this' has been changed to refer to subObj1.This is a problem as now method1 has lost all connection with its object obj1.If I define method1 within the 'Class1' function, I can get it to work if I use the 'var me = this;' trick, but if you have lots of methods within Class1() with further nesting this can get a bit hard to read.So, can someone tell me how to deal with 'this' changing. I.e. I want 'this' to refer to obj1 within method1.
<html>
<body>
<script type="text/javascript">
[code]....
On another note, there seems to many ways of defining methods (e.g using 'prototype' etc etc) and I gettting sick and tierd of a 'trial and error' approach to get things working. Can anyone recomend a good resourse that sets out the best way to design with javascript so I dont keep running into these issues.
I got following document:
When you click the main button, will one of the six images get a background image, and you can then press the image with the background image, and get your "reflextime".
But it won't work. When I press the image, were the new background image has shown, you can click on it and get your time - why?'