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?
Normally, 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 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?
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 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]....
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 RelatedI 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 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 written a number of functions designed to return frequency data on 1000 randomly chosen numbers using different math functions for the rounding. I would like to include all of these functions within the wrapper of another function so that only one call is needed to get returns from all of the 'inner' functions. However, while each of the functions works in isolation, the moment I wrap them in another function they stop working. :confused:
The following code is one of the functions 'frequencyWrapperOne' that has been wrapped in the function 'testWrapper'. A call to testWrapper does nothing.
function testWrapper()
{
function frequencyWrapperOne()
{
[Code]....
$(something).split(something),this is a function with a function as a property for that function.
View 8 Replies View Relatedhow about getting the attributes of the a tag? href and title and the innerhtml (actually the innerhtml has space on both ends)
View 4 Replies View RelatedI have several form in my site, that validate on onsubmit.I call all the validation functions from a file call functions.js.Here is a sample of the code that is working:
<form name="contact" action="contact-insert.php method="post" onSubmit="return checkform()">
<label class='SubHeadlbl' for='TextField1'><?php echo IDS_EFORMNAME?><br></label>
<input type='text' name='dfname' class='text_field' id='dfname1' size='70' maxlength='40'/>
</form>
all the other forms are not working. all have the same structure:
<form name="frm1000" action="frm1000-insert.php method="post" onSubmit="return checkform1000()">
<label class='SubHeadlbl' for='TextField1'><?php echo IDS_EFORMNAME?><br></label>
<input type='text' name='dfname' class='text_field' id='dfname1000' size='46' maxlength='40'/>
</form>
I don't know what is happening only one for work all the others don't.
Is it possible to take an ASP textbox that has an attribute of
visible='hidden' and make it visible from javascript? I dont want it
to be visible until data on the page has been entered and thus need a
way to dynamically change its visibility?
Can someone tell me if there is a universal way to check the available
screen with and screen height for IE, Netscape, and Opera? Is there a
universal syntax?
I'm using a jquery plugin called jplayer. I need to "bookmark" the current track.
The only way to know the current file playing is to look at the div called jplayer_playlist_current.
<li class="jplayer_playlist_current">
<a href="#" id="jplayer_playlist_item_1" class="jplayer_playlist_current">Introduction and guidance on usage</a></li>
What I want to get from it is the id, ie: jplayer_playlist_item_1
I thought that this might cover it:
[URL]
But nothing I do, no amount of googling or plugins, is getting me this result.
I want to move a div around a page, and I do this by getting the original top and left values of a div, and then change them. But the problem is getting the original values; I checked online and thought that this would work:
var chart = document.getElementById(charDiv).style.top;
var charl = document.getElementById(charDiv).style.left;
alert('char_t:' + chart + ' char_l:' + charl + 'charDiv:' + charDiv);
charDiv is passed into the function (its the id of the div I want to move). I know that charDiv has a value by looking at the values of the alert() statement, but the values of chart and charl are empty. The alert simply outputs char_t: char_l: charDiv: charOne