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If Checkbox is checked, remove attribute?

<div class="span1">
<input type="checkbox" value="l4" id="l4" field="" defaultValue="" appEditor="true"/>
</div>
<div class="span7">
<input type="text" class="m-wrap span10" id="fld_l4" defaultValue="" editType="intEdit" appEditor="true" disabled />
</div>
What I want to do is, If checkbox is checked, remove disabled in the fld_l4.
How to do this with using Prototype.js or jQuery?
EDIT: I'm using prototype with jQuery
i'm getting an error: Uncaught InvalidStateError: An attempt was made to use an object that is not, or is no longer, usable. By the way i replaced $ with jQuery for conflicts
EDIT2 : Solved.
this.l4 = editor.instance;
editor.observe(iconstants.KEY_CHANGE,this.levelCheckboxChanged.bindAsEventListener(this))
Inside levelCheckboxChanged:
levelCheckboxChanged: function(e) {
if($("l4").checked == false) {
$("fld_l4").disabled = true;
} else {
$("fld_l4").disabled = false;
}
},

You can do it like this
$('#l4').change(function(){
if(this.checked){
$("#fld_l4").removeAttr('disabled');
}
})
Demo Link

This way should work:
$("#l4").on("change", function () {
$("#fld_l4").prop("disabled", !$(this).is(":checked"));
});
jsFiddle: http://jsfiddle.net/J5Nt2/1/

Here is the way to do this with PrototypeJS
inside of your DOM loaded event
document.observe('dom:loaded',function(){
$('l4').observe('click',function(){
$('fld_l4').writeAttribute('disabled',this.checked);
});
});
Plus you might want to change the id of '14' browsers do not like you starting id's with numbers - they let you do it but it is not part of the HTML spec

Try this,
if( $("#l4:checked").length ) {
$("#fld_l4").removeAttr("disabled");
}

Try this:
if( $("#l4").is(":checked") ) {
$('#fld_l4').removeAttr('disabled');
}

How to display message with the help of jquery?

i m trying to do a validation using jquery.
Enter Account no:
here is my html code
<input type="text" name="Assets" id="Assets" size="25" /><br />
<div id="eb"> Please Enter Valid Account no </div>
Enter Amount<input type="text" name="Liability" id="Liability" size="25" /><br />
and here is my jquery code
$(document).ready(function(){
$("#Assets").change(function(){
var Assets = $('input#Assets').val();
var expression=/[0-9]{4}\s[0-9]{4}\s[0-9]{2}\s[0-9]{10}/;
if (Assets == "" || Assets == " ") {
$('#eb').show();
}
else if(Assets.test(expression)){
$('#eb').hide();
}
$('#eb').toggle();
}
i want to display a mesage when user write a account no then at a time he can see the message that Please Enter Valid Account no and if he insert correct then that message can be hide.
here is my jsfiddle - http://jsfiddle.net/BzdfN/5/
please help

Try this code:
$(document).ready(function () {
$("#Assets").change(function () {
var Assets = this.value;
var expression = /[0-9]{4}\s[0-9]{4}\s[0-9]{2}\s[0-9]{10}/;
if (Assets.match(expression)) {
$('#eb').hide();
} else {
$('#eb').show();
}
});
});
This is a suggestion for more simple code. Notice I used match() which takes a regex as paramenter, if you want to use test() you should use the value/string as paramenter and use like expression.test(Assets).
Fiddle
About your code/fiddle:
you missed adding jQuery library to the fiddle
you missed ) closing the change() function
you missed }) closing the ready() function
you used test() with wrong order, check my text above about match() and test()
your fiddle with corrections: Fiddle

jQuery was not included and multiple syntax errors
$(document).ready(function () {
var expression = /[0-9]{4}\s[0-9]{4}\s[0-9]{2}\s[0-9]{10}/;
$("#Assets").change(function () {
$('#eb').toggle(!expression.test(this.value));
})
})//missing brackets
Demo: Fiddle

Try this - http://jsfiddle.net/dangoodspeed/BzdfN/9/ I made a bunch of changes, including activating jQuery, closing some functions, and reversed Assets and expression for the .test call
else if(expression.test(Assets)){

How to clear a text field?

I want to place a cross button next to a text field, which, on clicking it, clears the value entered by the user. In other words, it empties the field. Please help..
And I also want to focus the field, but after some 2 or 3 seconds..

Like this:
$('#myButton').click( function () {
$('#myField').val('');
});
Or without jQuery
document.getElementById('myButton').onclick = function () {
document.getElementById('myField').value = '';
});

Try this,
$('#button').click(function(){
$('#inputBox').val('');
});

Have you tried anything at all? But this should do (edit after misread, see below):
$('#your_button').click(function() { $('#your_textbox').val(''); });

In Javascript:
document.getElementById('textField1').value = "";

Well, learn to break your tasks into smaller one and everything will become much easier. Here, for example, you have 2 tasks:
1) Place a "X" button near input. This is achieved by CSS and HTML. You HTML might look like:
Then you should align your image with you input
2) Actual erasing. In jQuery:
$("#x_button").click( function() {
$("#input_id").val( "" );
});
But this is real basics of web development, so you should really consider to read some kind of book on it.

You can do it with html5 value.
<input type="text" placeholder="Your text here">

Assuming your text field looks like this one :
<input type="text" id="myText"></input>
and your button looks like this one :
<input type="button" id="myButton"></input>
You just have to do this in javascript :
<script type="text/javascript">
var myButton = document.getElementById('myButton');
myButton.addEventListener("click", function () {
document.getElementById('myText').value = '';
}, false);
</script>
If you're using jQuery it's even easier :
<script type="text/javascript">
$('#myButton').click(function() {
$('#myText').val('');
});
</script>

here is a sample:
Html:
<input type="text" id="txtText" value="test value" />
<input type="button" id="btnClear" value="Clear" />
javascript:
$(document).ready(function () {
$("#btnClear").click(ClearText);
});
function ClearText() {
$("#txtText").val("");
}

Checkbox to change font weight not working - Javascript

I need to insert a checkbox into a form to change the font weight of text in a div.
My javascript is as follows:
function boldText(checkBox,target) {
if(checkBox.checked){
document.getElementById("lineOne").style.fontWeight = "bold";
}
else {
document.getElementById("lineOne").style.fontWeight = "normal";
}
}
And my html like so:
<input type="checkbox" onclick="boldText(this,textToBold)">
<div id="lineOne">Change text to bold</div>
What is wrong here. I cant seem to get it to work.

remove target it is undefined so it gives an error send id of div in single quate as follow
<script>
function boldText(checkBox,target){ if(checkBox.checked){
document.getElementById(target).style.fontWeight = "bold"; }
else
{ document.getElementById(target).style.fontWeight = "normal"; } }
</script>
<input type="checkbox" onclick="boldText(this,'lineOne')">
<div id="lineOne">Change text to bold</div>
refer jsfiddle

Just delete target in function argument and textToBold when you call it

http://jsfiddle.net/xArCc/1/
or
http://jsfiddle.net/xArCc/2/
There you go. The target should've been "lineOne" when you make the call.

Change this line to :
<input type="checkbox" onclick="boldText(this,'textToBold')">
Because "textToBold" is a string.

Javascript Form Submit Failure

I have code on my website that isn't working, and I haven't been able to figure out why...
Here is the code:
if (self.location.href == top.location.href) {
document.fastform.submit();
document.getElementById(fastform).submit();
}
Now if I put something other than a form submit into the if statement, it works just fine. It's just when I do the form submit code it never works...
Here is the form code:
<form id="fastform" name="fastform" ACTION="/amember.php">
<INPUT TYPE="text" NAME="myurl" ID="myurl">
<input type="submit" />
</form>
Thanks for the help guys!
So far none of the suggestions work, I have tried several different variations like putting quotes around the fastform in getelementbyid. Here is my entire javascript program:
<script type="text/javascript">
function geturl() {
var locate = document.location
document.fastform.myurl.value = locate
}
window.onload = geturl;
if (self.location.href == top.location.href) {
var f=document.forms.fastform; f.submit();
}
</script>
Thanks for the suggestions!
Okay, so using some of the suggested code here I got it working. The problem was the if statement was not being executed at the right time, I moved things around so that the if statement was executed LAST and everything started working. Here is the complete (functioning) code:
<script type="text/javascript">
function geturl() {
var locate = document.location
document.fastform.myurl.value = locate
getmeoutofhere()
}
window.onload = geturl;
function getmeoutofhere() {
if (self.location.href == top.location.href) {
document.getElementById('fastform').submit();
}
}
</script>
<form id="fastform" name="fastform" ACTION="/amember.php" style="visibility:hidden;">
<INPUT TYPE="text" NAME="myurl" ID="myurl" />
<input type="submit" />
</form>

You can use this in your function:
var f=document.forms.fastform;
f.submit();
and it's working completely fine

document.getElementById('fastform').submit();
OR
var frm = document.getElementById('fastform');
frm.submit();

I'm not sure if it's the problem, but there's certainly one problem with the line:
document.getElementById(fastform).submit();
The problem, I think, is that you're trying to get an element by its id, but getElementById() requires a quoted string, unless you've already assigned the string to the variable represented by fastform. Therefore it should be either:
document.getElementById('fastform').submit();
or:
var fastform = 'fastform';
document.getElementById(fastform).submit();
Further, you seem to be trying to work with the fastform variable before it seems to have been set, in the first line contained within the if statement:
document.fastform.submit();
I'd suggest amending your script a little, to be something like:
if (self.location.href == top.location.href) {
var fastform = document.getElementById('fastform');
fastform.submit();
}
References:
document.getElementById().