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How to set radio button value as checked or unchecked situation

<input type="radio" name="imgsel" value="" checked />
My requirement is : This radio button by default checked then value of this button is 'present'. When this button is unchecked , then value this button is 'absent'.
how can i do this?
please, help me .
Thanks in advance .

function valChange(element)
{
if (element.checked)
{
alert("present");
} else
{
alert("absent");
}
}
<input id="button" type="checkbox" name="imgsel"
onchange="valChange(this)" value="" checked />

The following example replaces the value of the checkbox when clicked.
First the click event must be bound to the checkbox. The EventHandler checks whether the box has already been checked. If not, it checks it and sets the value in the checkbox. And if it has not been checked, the other way round.
let i = document.querySelector('input');
i.addEventListener('click', (ev) => {
let el = ev.target;
if (el.getAttribute('checked') === null) {
el.setAttribute('checked', true);
el.value = "present"
} else {
el.removeAttribute('checked');
el.value = "absent"
}
let checkValue = document.querySelector('input').value
alert(checkValue)
})
<input type="radio" name="imgsel" value="" checked />

Checkbox check or uncheck value null

I'm trying to set the value of a checkbox, if checked the value is active, but if unchecked the value is disabled.
The next code works for text, the text changes when the checkbox is checked or unchecked, but the value that is posted to the database is null when the checkbox is unchecked.
HTML
<input type="checkbox" name="cat_status" class="inline checkbox" id="checkbox" checked value="active" onclick="cat_check()">
<label id="text" style="display:Active">Active</label>
JS
function cat_check() {
var checkBox = document.getElementById('checkbox');
var text = document.getElementById('text');
if (checkBox.checked == false) {
text.style.display = "inline";
document.getElementById('checkbox').value = "active";
} else {
text.style.display = "none";
document.getElementById('checkbox').value = "disable";
}
}
I expect the value posted to database to be disabled when the checkbox is unchecked, but currently getting a null.
Update:
Added a fixed version including the AJAX call based on the provided feedback of the answers. This is just in case someone fall into the same issue.
If you play with the example on the bottom of serialize() documentation you will see that value is not appended for checkboxs that are uncheked. You will have to do it manually. Maybe this can help you: how can I override jquery's .serialize to include unchecked checkboxes
HTML
<form method="post" class="add_sub_categories">
<input type="checkbox" name="cat_status" class="inline checkbox" id="checkbox" checked value="active" onclick="cat_check()">
<label id="text" style="display:Active">Active</label>
<a class="btn btn-xs btn-info save_main_cat">GO!</a>
</form>
JS
function cat_check() {
var checkBox = document.getElementById('checkbox');
var text = document.getElementById('text');
if (checkBox.checked == true) {
text.style.display = "inline";
} else {
text.style.display = "none";
}
}
AJAX
$(document).ready(function() {
$(".save_main_cat").click(function() {
var data = $('.add_main_categories').serialize();
/* This code will include the value for the checkbox when unchecked */
$(".add_main_categories input:checkbox:not(:checked)").each(function(e) {
data += "&"+this.name+'=disable';
});
$.ajax({
type: 'POST',
url: "<?= base_url() ?>admin_ajx/categories_ajx/update_main_categories",
data: data,
success: function() {
$('#addCat').modal('hide');
$(".add_main_categories")[0].reset();
dttable.destroy();
$(document).ready(function() {
main_cat(), main_cat_option(), dt_tables();
});
}
});
});
});

If I understood correctly, the problem is on your click handler. When you unchek the checkbox by clicking on it, the checked property will be false when you observe it inside the click handler. And you are doing this:
if (checkBox.checked == false)
{
text.style.display = "inline";
document.getElementById('checkbox').value = "active";
}
So, in other words, you are setting the value to active when the checkbox is unchecked, but instead, that setting should be associated to checked state equal to true. I believe you are looking for something like this:
function cat_check()
{
var checkBox = document.getElementById('checkbox');
var text = document.getElementById('text');
if (checkBox.checked === true)
{
text.style.display = "inline";
checkBox.value = "active";
}
else
{
text.style.display = "none";
checkBox.value = "disable";
}
console.log(checkBox.value);
}
.as-console {background-color:black !important; color:lime;}
<input type="checkbox" name="cat_status" class="inline checkbox" id="checkbox" checked value="active" onclick="cat_check()">
<label id="text" style="display:inline">Active</label>
There are other fixs on the code also:
A) The initial display:Active is not a valid CSS configuration in reference to <label id="text" style="display:Active">Active</label>. So I changed it to display:inline.
B) Use the already defined variable checkBox inside the click handler instead of doing multiple calls to document.getElementById('checkbox').

You can set value 1 , as if it is checked then value posts 1 otherwise can checked null or not;
// In view
//On post time you can check if value is 1 then cheked otherwise null

Unchecking of the checked checkboxes on another button click

I want the checked checkboxes to be unchecked when clicking another button:
Below is the HTML
<input type="checkbox" name="checkb" id="Agent" value="Agent"> type=Agent
<br />
<input type="checkbox" name="checkb" id="Customer" value="Customer"> type=Customer
<br />
<input type="checkbox" name="checkb" id="Phone" value="Phone"> type=Phone
<br />
<input type="checkbox" name="checkb" id="ID_Card" value="ID_Card"> type=ID_Card
<br />
<input type=datetime id="Start_Date" value="" placeholder="Start_Date" />
<input type=datetime id="End_Date" value="" placeholder="End_Date" />
<button id="date">
Interval
</button>
On clicking of the Interval button if any checkboxes are checked they should get unchecked.
Below is the event listener for the Interval button:
var check1 = document.getElementById("Agent");
var check2 = document.getElementById("Customer");
var check3 = document.getElementById("Phone");
var check4 = document.getElementById("ID_Card");
var newBtn = document.getElementById("date");
if (newBtn) {
newBtn.addEventListener("click", function() {
if (check1.checked) {
var ischecked1 = check1.checked;
check1.checked != ischecked1;
}
if (check2.checked) {
var ischecked2 = check2.checked;
check2.checked != ischecked2;
}
if (check3.checked) {
var ischecked3 = check3.checked;
check3.checked != ischecked3;
}
if (check4.checked) {
var ischecked4 = check4.checked;
check4.checked != ischecked4;
}
});
}
Below code runs without any errors, but the boxes do not get unchecked if they are checked.
Below is the fiddle

Your statements are just evaluating as booleans, not performing assignments:
check1.checked != ischecked1; // this returns a boolean, doesn't do any assignment
You want to do this to toggle the checked state:
check1.checked = !ischecked1;
Same thing for other checkboxes.
There's also no need to create the extra variables, you can just do the toggling and reading directly:
check1.checked = !check1.checked;
Since you're only toggling checkboxes when they are checked, you can just directly set them to false as well.
if (check1.checked) check1.checked = false;
Instead of having if statements, you can use array iteration to do the toggling:
[check1, check2, check3, check4].forEach(check => {
if (check.checked) {
check.checked = false;
}
});
// or query the checkboxes directly and do the same
[...document.querySelectorAll('input[type="checkbox"]')].forEach(check => {
if (check.checked) {
check.checked = false;
}
});

Your mistake is in this line:
check1.checked != ischecked1;
This actually means "compare if check1.checked is not equal to ischecked1".
Most simple solution would be to remove the if statement and just do this:
check1.checked = !check1.checked
This means "set check1.checked to the opposite of check1.checked".
Since all checkboxes have the same name you could also collect all checkboxes by requesting them by name and use a loop to walk through them. A small example:
// Collect all checkboxes with a CSS selector that matches all input
// elements with a name attribute that's equal to "checkb"
var checkboxes = document.querySelectorAll('input[name="checkb"]');
var newBtn = document.getElementById("date");
if (newBtn) {
newBtn.addEventListener("click", function() {
// this is a for loop, it will run for as long as i
// is smaller than the amount of found checkboxes (checkboxes.length)
for(var i = 0; i < checkboxes.length; i++) {
// Get the checkbox from the checkboxes collection
// collection[i] means get item from collection with index i
var checkbox = checkboxes[i];
// Revert the .checked property of the checkbox
checkbox.checked = !checkbox.checked;
}
});
}

By the looks of it you just want to uncheck everything on click of button
you can just do this
var newBtn = document.getElementById("date");
if (newBtn) {
newBtn.addEventListener("click", function() {
document.getElementById("Agent").checked =
document.getElementById("Customer").checked =
document.getElementById("Phone").checked =
document.getElementById("ID_Card").checked = false;
});
}

unselecting radio input selection

In a part of my application where i check for duplicate radio input selection and revert if its already selected to early selection.
Here is my html code ..
<input type="radio" name="A" checked="checked" onclick="return check();" />
<input type="radio" name="A" onclick="return check();" />
<br />
<input type="radio" name="B" onclick="return check();" />
<input type="radio" name="B" checked="checked" onclick="return check();" />
Here is the javascript code
function check() {
//logic to check for duplicate selection
alert('Its already selected');
return false;
}
And here is the demo
The above code works fine. The issue is when the input isn't initially checked. In such condition the radio input selection doesn't revert to unchecked.
NOTE: when in checked state, returning false shows and alert and sets the check box to initial checked state. But when initially in non checked state this doesn't work.

In DOM ready, check if any radio button is checked or not. If any radio button is checked, increase the counter by one. In onclick of the radio button, check if the counter value is 1. if yes, return false, else increase counter by 1.
try this code,
html
<input type="radio" name="A" checked="checked" />
<input type="radio" name="A" />
<br />
<input type="radio" name="B" />
<input type="radio" name="B" />
JS
var counterA = 0;
var counterB = 0;
$(document).ready(function () {
if ($("input:radio[name=A]").is(":checked") == true) counterA++;
if ($("input:radio[name='B']").is(":checked") == true) counterB++;
});
$('input:radio[name=A]').click(function () {
if (counterA == 1) {
alert('already checked');
return false;
} else {
counterA++;
}
});
$('input:radio[name=B]').click(function () {
if (counterB == 1) {
alert('already checked');
return false;
} else {
counterB++;
}
});
SEE THIS DEMO

iJay wants to ask several questions and privides the same answers for each question. Each answer can only be choosen once. If a user clicks the same answer the second time a error-message should be shown.
// get all elements
var elements = document.querySelectorAll('input[type="radio"]');
/**
* check if radio with own name is already selected
* if so return false
*/
function check(){
var selected_name = this.name,
selected_value = this.value,
is_valid = true;
// compare with all other elements
for(var j = 0; j < len; j++) {
var el = elements[j];
// does the elemenet have the same name AND is already selected?
if(el.name != selected_name && el.value == selected_value && el.checked){
// if so, selection is not valid anymore
alert('Oups..! You can not select this answer a second time :( Choose another one!')
// check current group for previous selection
is_valid = false;
break;
}
};
return is_valid;
}
/**
* bind your elements to the check-routine
*/
for(var i = 0, len = elements.length; i < len; i++) {
elements[i].onmousedown = check;
}
Here is a DEMO

Use $yourRadio.prop('checked', false); to uncheck the specific radio.

Use like this:
function check() {
//logic to check for duplicate selection
var checked = true ? false : true;
$(this).prop('checked', checked);
return false;
}

1) add class attribute to same type of checkbox elements(which are having same name)
ex: class = "partyA"
2)
var sourceIdsArr = new Array();
function check() {
$('.partyA').each(function() {
var sourceId = $(this).val();
if(sourceIdsArr.indexOf(sourceId) != -1){
sourceIdsArr.push(sourceId );
}
else{
alert('Its already selected');
return false;
}
});
}

Here is your code..
function check() {
//logic to check for duplicate selection
var selectflag=0;
var radiovalue=document.getElementsByName("B");
for(var i=0;i<radiovalue.length;i++)
{
// alert(radiovalue[i].checked);
if(radiovalue[i].checked==true)
{
selectflag=1;
break;
}
}
if(selectflag==1)
{
alert('Its already selected');
return false;
}
return true;
}
Trigger your event on MouseDown. It will work fine.

I think this is something you are looking for :
<html>
<head>
<script src="http://code.jquery.com/jquery-1.11.0.min.js"></script>
</head>
<body>
<input type="radio" name="A" checked="checked" onclick="return check(this);"/>
<input type="radio" name="A" onclick="return check(this);"/>
<script>
$( document ).ready(function() {
this.currentradio = $("input[name='A']:checked")[0];
});
function check(t) {
var newradio= $("input[name='A']:checked")[0];
if (newradio===document.currentradio){
alert('already selected');
return false
}else{
document.currentradio = $("input[name='A']:checked")[0];
}
}
</script>
</body>
<html>

Javascript checkbox onChange

I have a checkbox in a form and I'd like it to work according to following scenario:
if someone checks it, the value of a textfield (totalCost) should be set to 10.
then, if I go back and uncheck it, a function calculate() sets the value of totalCost according to other parameters in the form.
So basically, I need the part where, when I check the checkbox I do one thing and when I uncheck it, I do another.

Pure javascript:
const checkbox = document.getElementById('myCheckbox')
checkbox.addEventListener('change', (event) => {
if (event.currentTarget.checked) {
alert('checked');
} else {
alert('not checked');
}
})
My Checkbox: <input id="myCheckbox" type="checkbox" />

function calc()
{
if (document.getElementById('xxx').checked)
{
document.getElementById('totalCost').value = 10;
} else {
calculate();
}
}
HTML
<input type="checkbox" id="xxx" name="xxx" onclick="calc();"/>

If you are using jQuery.. then I can suggest the following:
NOTE: I made some assumption here
$('#my_checkbox').click(function(){
if($(this).is(':checked')){
$('input[name="totalCost"]').val(10);
} else {
calculate();
}
});

Use an onclick event, because every click on a checkbox actually changes it.

The following solution makes use of jquery. Let's assume you have a checkbox with id of checkboxId.
const checkbox = $("#checkboxId");
checkbox.change(function(event) {
var checkbox = event.target;
if (checkbox.checked) {
//Checkbox has been checked
} else {
//Checkbox has been unchecked
}
});

HTML:
<input type="checkbox" onchange="handleChange(event)">
JS:
function handleChange(e) {
const {checked} = e.target;
}

Reference the checkbox by it's id and not with the #
Assign the function to the onclick attribute rather than using the change attribute
var checkbox = $("save_" + fieldName);
checkbox.onclick = function(event) {
var checkbox = event.target;
if (checkbox.checked) {
//Checkbox has been checked
} else {
//Checkbox has been unchecked
}
};

Javascript
// on toggle method
// to check status of checkbox
function onToggle() {
// check if checkbox is checked
if (document.querySelector('#my-checkbox').checked) {
// if checked
console.log('checked');
} else {
// if unchecked
console.log('unchecked');
}
}
HTML
<input id="my-checkbox" type="checkbox" onclick="onToggle()">

try
totalCost.value = checkbox.checked ? 10 : calculate();
function change(checkbox) {
totalCost.value = checkbox.checked ? 10 : calculate();
}
function calculate() {
return other.value*2;
}
input { display: block}
Checkbox: <input type="checkbox" onclick="change(this)"/>
Total cost: <input id="totalCost" type="number" value=5 />
Other: <input id="other" type="number" value=7 />

I know this seems like noob answer but I'm putting it here so that it can help others in the future.
Suppose you are building a table with a foreach loop. And at the same time adding checkboxes at the end.
<!-- Begin Loop-->
<tr>
<td><?=$criteria?></td>
<td><?=$indicator?></td>
<td><?=$target?></td>
<td>
<div class="form-check">
<input type="checkbox" class="form-check-input" name="active" value="<?=$id?>" <?=$status?'checked':''?>>
<!-- mark as 'checked' if checkbox was selected on a previous save -->
</div>
</td>
</tr>
<!-- End of Loop -->
You place a button below the table with a hidden input:
<form method="post" action="/goalobj-review" id="goalobj">
<!-- we retrieve saved checkboxes & concatenate them into a string separated by commas.i.e. $saved_data = "1,2,3"; -->
<input type="hidden" name="result" id="selected" value="<?= $saved_data ?>>
<button type="submit" class="btn btn-info" form="goalobj">Submit Changes</button>
</form>
You can write your script like so:
<script type="text/javascript">
var checkboxes = document.getElementsByClassName('form-check-input');
var i;
var tid = setInterval(function () {
if (document.readyState !== "complete") {
return;
}
clearInterval(tid);
for(i=0;i<checkboxes.length;i++){
checkboxes[i].addEventListener('click',checkBoxValue);
}
},100);
function checkBoxValue(event) {
var selected = document.querySelector("input[id=selected]");
var result = 0;
if(this.checked) {
if(selected.value.length > 0) {
result = selected.value + "," + this.value;
document.querySelector("input[id=selected]").value = result;
} else {
result = this.value;
document.querySelector("input[id=selected]").value = result;
}
}
if(! this.checked) {
// trigger if unchecked. if checkbox is marked as 'checked' from a previous saved is deselected, this will also remove its corresponding value from our hidden input.
var compact = selected.value.split(","); // split string into array
var index = compact.indexOf(this.value); // return index of our selected checkbox
compact.splice(index,1); // removes 1 item at specified index
var newValue = compact.join(",") // returns a new string
document.querySelector("input[id=selected]").value = newValue;
}
}
</script>
The ids of your checkboxes will be submitted as a string "1,2" within the result variable. You can then break it up at the controller level however you want.