Variable Scope In Onclick Event
Oct 17, 2010
I have this web application where users are able to fill out and submit reports. The reports and scripts are part of a whole system, that is, they are used on a couple of different clients written in both vb and c#. This is the web-version of those clients.The scripting language is javascript and is executed using different script engines on the different systems. But for the web-version it is just executed in the browser.The different fields in the report can be accessed by typing:ID1.value. To get ID1 to apply for the input-field with id ID1 I had to in the initfunction of the page write a window["ID1"] = document.getElementById("ID1");
But my problem is when this element change. Cause in the report I have a special element that in the browser is translated to a table-element with a report-field in each cell.When I switch the current row, I need to update the window["ID1"] to equal the correct report field on the selected row. But when trying to access the new variable ID1 from a buttons onclick event it is undefined.<input type="text" id="test" onclick="alert(ID1.value);" />What I think happens is that when the page is first drawn the onclick event is created and as I understand, variables inside an event has the same value as when the event was created.
So if ID1.value was something when the page was created it will be the same when it is called even if the value of ID1 is different. And that seems to be the case. When I debug the page, before entering the event, ID1.value has the correct value while inside the event it is undefined and after the event it has the correct value. If I write window["ID1"] correct value is also shown.But a weird thing is that in another place in the code I had the same problem but instead of having the code inside the onclick event I first had a global function changeActiveRow and inside that I had an eval, eval(document.getElementById("ID1_script")) where ID1_script is a hidden element whos value is a script using ID1.value and that works.
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Mar 20, 2011
what i want to do-
$
(
"#temp"
).
[Code]....
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Sep 11, 2009
I have a html page with a lot of thumbnails. The idea is that when the user clicks on an image the onClick event is to display another detailed form and deliver to that form the name of the image in a variable. In the detailed php-form there is a query to MySQL to retrieve a record. The record will be retrieved by a Query based on the name of the picture. Apparently the PHP cannot do the job. I had an idea to make the thumbnail page as a form and to use use a hidden field with the thummnail name which should be carried on with the $_POST array through the submit button but i do not want to have a submit button. The more elegant way is just by clicking the picture the detailed page is opened and the variable is transferred where my php code can make use of the variable for the query. I have never used java before so you have to excuse for the lack of knowledge.
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Dec 13, 2011
i'm having a slight problem understand how to use this.myVar in an object. And I use prototype.
[Code]...
Does anyone know how I can use this.myvar within the function. I have tried binding and bindAsEventListener.But nothing I've done has been able to get the right value!
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Jul 20, 2005
If I do . . .
myForm=document.tstForm;
function initialSetup(){
myForm.fld01.value="Test 01"
myForm.fld02.value="Test 02";
myForm.fld01.focus();
}
Then, in the body tag, I do onLoad="initialSetup()",
the script doesn't work and I get a "myForm has no properties" error
I know it'll work if I move it within the function, but I figured a
global variable would retain its value within the function. Why not?
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Jul 23, 2005
Given the following working code:
function attributes() {
var attr1 = arguments[0] || '_'
var attr2 = arguments[1] || '_'
return (
function (el1, el2) {
var value1 = el1[attr1] + el1[attr2];
var value2 = el2[attr1] + el2[attr2];
if (value1 > value2) return 1;
else if (value1 < value2) return -1;
else return 0;
}
);
}
var a = [
{ a:'smith', b:'john' },
{ a:'jones', b:'bob' },
{ a:'smith', b:'jane' }
];
a.sort(attributes('a', 'b'));
for (var i =0; i < a.length; i++) {
document.write(a[i].a + ', ' + a[i].b + '<br>');
}
My question is, are attr1 and attr2 guaranteed to exist through
the lifetime of a.sort(attributes('a', 'b'))?
As I understand it, the anonymous inner function reference I am
returning is a property of attributes(). As such, when I return a
reference to the anonymous inner function, the outer attributes()
function must continue to exist (as must attr1 and att2) until
there are no further references to the inner anonymous function.
As a result, there is no danger of attr1 or attr2 "disappearing"
during the repeated calling of the anonymous inner function.
Is my explanation basically correct, or am I deluding myself and
I'm just lucky that the garbage collector hasn't recovered attr1
or attr2 while the sort is still going on? In other words, is the
behaviour I'm seeing consistent and predictable, or should I
change my approach?
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Oct 30, 2006
I think I've had JavaScript variable scope figured out, can you please
see if I've got it correctly?
* Variables can be local or global
* When a variable is declared outside any function, it is global
regardless of whether it's declared with or without "var"
* When it is declared inside a function, if declared with "var", it's
local, if not, it's global
* A local variable that is declared inside a function is local to the
whole function, regardless of where it is declared, e.g.:
function blah() {
for(var i ... ) {
var j ...
}}
i and j will both be visible within blah() after their declaration.
* the notion of "function" in this context also applies for this kind
of construct:
var myHandler =
{
onClickDo: function()
{
in the sense that whatever one declares inside onClickDo with "var"
will only be visible inside onClickDo. What else, am I missing anything?
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Jun 14, 2010
I've created a jQuery script that uses a switch statement. However, my experience with it, relative to variable scope, doesn't seem to follow the logic.According to the JavaScript/jQuery theory, a global variable was accessible (meaning read & write) throughtout any function within any script (one that page).However, apparently that theory wasn't completely true as it pertained to switch statements that contained variables. To illustrate my case in point, I've included a simplistic version of my code:
$("#selector").delegate("div", "click", function(event) {
var testVar = 4;
switch (this.id) {
[code]...
As shown, the variable "testVar" is not accessible from one case to the next case .Furthermore, to add insult to injury, I am seeing the same behavior within the conditional if else statement counterpart to the switch statement.
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Jul 23, 2005
I have a script in which a function launched by a START button
continuously calculates and writes a value to a text box. The
calculation is done in a for loop. In the loop is a conditional that is
a global variable, a boolean. If the boolean is true, break ends the
loop (or is supposed to!). A STOP button has an onclick function that
sets the global variable to true.
What happens, though, is that the function for the STOP button is
not executed until the for loop reaches the maximum value set for i.
Anyone know how you can get one button to stop a process started by
another?
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Nov 23, 2005
I am trying to convert some of my javascripts into a class and am
running into difficulties which i think are related to variable scope.
Basically I have a constructor function for a calendarInput class that
takes 4 parameters, the first is a reference name/number for this
input. I also have some functions for importing my PHP classes into
Javascript using AJAX (properties only. still trying to get methods
working but that's another story!). The relevant function is called
call_object_method(classname, methodname, createparams, methodparams,
post, callbackfunction). This creates an instance of the specified PHP
class using the parameters in createparams. It then calls the
specified method using the parameters in methodparams. The result is
passed back to the javascript function specified in the callbackfunction parameter (ie the value of xmlhttp.onreadystatechange is set to callbackfunction before xmlhttp.send() is called)
The function i am trying to fix is called show (x,y) which creates the
html for the calendarInput and displays it at co-ordinates x, y.
So, my code is as follows:
function calendarInput(calendarid, target, displaytarget, value)
{
this.calendarid = calendarid;
this.target = target;
this.displaytarget = displaytarget;
this.value = value;
this.show = function(x, y)
{
<!--// bunch of init and prepping code. includes creating
createparams and methodparams arrays //-->
call_object_method("cms_calendar", "getcalendarview",
createparams, methodparams, false, this.showcallback);
}
this.showcallback = function()
{
alert(this);
<!--//code to create html//-->
}
}
I know i've cut out most of the innards of this. This is because I
have already tested these functions and had the calendarInput working
outside of a class, hence am pretty sure that this is ok (plus it runs
to almost 1000 lines these days!!). My problem is that when I call the
show method, the alert on the first line of the callback function
returns the function showcallback instead of (as i was expecting) the
instance of the calendarInput object. Whilst this kinda makes sense I
can't figure out how to reference the Object instead. I have tried
'this.parent' but this returned undefined. I have tried changing the
way i reference the callback function (ie the final parameter of
call_object_method) but no joy.
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Aug 23, 2010
I've recently started developing javascript using jQuery and so far I'm really enjoying it.Being a professional programmer (mainly C, C++, java and python) there is one thing that's been puzzling me regarding variable scope and unnamed function declarations. Let me exemplify:
------------------------
var sum = 0;
$(xmlobj).find("item").each(function(){
[code]....
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Oct 27, 2009
I'm just starting out with Javascript as a development language and this will probably be a relatively simple problem for someone to solve for me.
I am trying to access a variable (this.bodyEl.innerHTML) from within a function but get an error message indicating that it is "undefined". I know that it is a valid variable because I call it elsewhere outside of the inner function itself.
I'm sure this is just a scope issue, but I'd welcome any suggestions on how to solve it with an explanation of where I've gone wrong if you have the time.
[Code]...
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Jan 31, 2011
[code]how i can set context/scope for myStartAction so it can access (this.url) variable?console.log(dd.url) will work but i can't predict what name will object have (that depends on user) there might be more than one instance of myObject
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Aug 11, 2004
Here's the situation: I have a javascript object for controlling a custom DHTML scrollbar. So that I can use more than one on a page, the event listeners need to be passed a reference to the particular instance of the object that each needs to connect to, but as I discovered the hard way, inside an event listener, 'this' returns a reference to the DOM object throwing the event, rather than to the JS object. Short of coming up with a linked list of different objects and having the event handler search through it for the right object when an event is generated, then writing a reference to that object to some global variable, is there any convenient way to tie this together? I hope I've made myself clear enough...
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Jul 25, 2011
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
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Feb 2, 2011
New to javascript/jquery and have a question regarding scope. I want to bind an event within my class so it calls one of the class methods. The problem I run into is that the event handler is a anonymous function that runs outside the scope of the class, therefore it doesn't see the class methods or properties.
Is there a proper way to deal with this:
Sample code:
function myObject(tag) {
// properties
this.myvar = 'test';
this.tag = tag;
// methods
function sendRequest() {
alert(this.myvar);
}
// initialization
$(this.tag).click( function() {
this.sendRequest();
});}
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Mar 23, 2010
I am using Ben Alman's JQuery resize plugin in order to obtain the varying computed width of an element when the window is resized (the element in question is a page wrapper that exhibits the expand-to-fit behavior of a block box, and it's computed width is obviously influenced by the resizing of the window. Essentially, what I need to be able to do, is to reference a variable that is defined in a .resize() function ('width_page') in a seperate .each() function.
[Code]...
I now understand that variables can't cross boundaries like in the example above, which leaves me a little stuck. I also understand that this is specific to the context of the .resize() function, and that it can't be taken out of it without using an element selector. Is there some way I can call the .resize() function in my .each() function?
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May 28, 2007
i'm not really sure how to explain this, since I know nothing about javascript, so i'll try and illustrate by the use of php (hope it makes sence)
I have a set of different links, like:
<a href="link.com?page=text1">text 1</a>
<a href="link.com?page=text2">text 2</a>
<a href="link.com?page=text3">text 3</a>
etc, where page is dynamic and can be anything I chose..
Another place in the same document, I echo out what the page variable is, like:
echo "$page";
so when clicking "text 1" the echo will output what i've defined the page to be, in this case "text1" ..
So I want to be able to click the links and change the output of the echo all depending on what i've defined in the link - without refreshing the page!
Is there any easy way to do this?
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Sep 4, 2010
I want to make it so that when I click on something, it changes what document.onclick does.
This is a simplified version of what I'm trying to do:
Code:
<div id="clickme" onclick="document.onclick = function(){ alert ('This should not be alerted on the first click'); }">Click here</div>
However, as you'll notice, the alert box shows up on the first click as well. The only way I have been able to get around this behaviour is to have the first onclick execute a timer that will then set the document.onclick after 1ms, however this seems very messy to me.
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Apr 4, 2010
I'm wanting a table cell click event to remove and replace the table it was clicked on, however I'm finding that as it's deleting the original table object the actual running event code is being replaced and the function is bailing.how I can call the delete/refresh function from outside the event's function scope?
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Jan 9, 2009
currently on our site we have and expanding <div> that responds to both the onmouseover and onmouseout events. It works wonderfully.
The UX people now would like the expanding <div> to open with the onclick event and then as soon as the mouse leaves the expanded div, it would close. I have tried using the onmouseout event in conjunction the onclick event but it does not work (the div persists).
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Jul 24, 2006
I am trying to apply the current value of variable i to the links onclick event
I've even tried assigning it to variable j but the only values I get when any link is clicked is
i = 5
j = 4
The "page"+i and "Link"+i show as they should with variable i showing the correct value. Code:
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Feb 20, 2005
I have a JS variable I want to write inside of a onclick="" attribute. Example:
<script>
var cool = "hello";
</script>
<a href="#" onclick="RunFunction(cool)">Text</a>
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Jan 16, 2009
I know how to pass a variable to a url using href.
(href="thisurl.php?thisvar=thisvalue")
now I want to do this using onClick, how do I?
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Apr 2, 2009
Basically, I have a form with some text fields, and I want to put a button next to each text field, so that when a user clicks on the button, it increments the value in the field by 1. I know how to do it if I know the id of the text field, but what if the id of the text field is a variable? How do I do it? Here's my code:
<script language=javascript>
function process(v){
document.getElementById('order_item' + v + '_quantity').value++;
[code]....
My issue is with my onclick statement:
<input type="button" value="Add +" onclick="javascript:process(0)">
This works fine for my first field, but I need to have one for every text field, so how do I pass my counter variable (which determines the id of the appropriate text field) to the process function?
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Apr 17, 2011
I have a book on my page consist of 3 iframes, 1 iframe opens the table of contents and 2 iframes to open 2 pages at the same time, also i have 2 buttons to navigate pages next and previous through this function
[Code]...
the problem starts here, if i click on next-previous button I want it to continue from page 36,37 but what happens it continue from pNum in the function, how to update the pNum from onclick ?
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