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Getting val() of last checkbox checked by a user [duplicate]

I have the following HTML:
<div class="pricing-levels-3">
<p><strong>Which level would you like? (Select 3 Levels)</strong></p>
<input class="single-checkbox"type="checkbox" name="vehicle" value="Bike">Level 1<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 2<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 3<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 4<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 5<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 6<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 7<br>
</div>
Live site:
http://www.chineselearnonline.com/amember/signup20.php
How can I do it so that the user can only select 3 of those checkboxes?

Using change event you can do something like this:
var limit = 3;
$('input.single-checkbox').on('change', function(evt) {
if($(this).siblings(':checked').length >= limit) {
this.checked = false;
}
});
See this working demo

Try like this.
On change event,
$('input[type=checkbox]').on('change', function (e) {
if ($('input[type=checkbox]:checked').length > 3) {
$(this).prop('checked', false);
alert("allowed only 3");
}
});
Check this in JSFiddle

Try this DEMO:
$(document).ready(function () {
$("input[name='vehicle']").change(function () {
var maxAllowed = 3;
var cnt = $("input[name='vehicle']:checked").length;
if (cnt > maxAllowed)
{
$(this).prop("checked", "");
alert('Select maximum ' + maxAllowed + ' Levels!');
}
});
});

$('.checkbox').click(function(){
if ($('.checkbox:checked').length >= 3) {
$(".checkbox").not(":checked").attr("disabled",true);
}
else
$(".checkbox").not(":checked").removeAttr('disabled');
});
i used this.

I think we should use click instead change
Working DEMO

$("input:checkbox").click(function(){
if ($("input:checkbox:checked").length > 3){
return false;
}
});

Working DEMO
Try this
var theCheckboxes = $(".pricing-levels-3 input[type='checkbox']");
theCheckboxes.click(function()
{
if (theCheckboxes.filter(":checked").length > 3)
$(this).removeAttr("checked");
});

I'd say like letiagoalves said, but you might have more than one checkbox question in your form, so I'd recommend to do like this:
var limit = 3;
$('input.single-checkbox').on('change', function(evt) {
if($('input.single-checkbox').siblings('input.single-checkbox:checked').length > limit) {
this.checked = false;
}
});

(function ($) {
$(document).ready(function () {
$(document).on("change", ".pricing-levels-3 input", function () {
var numberOfChecked = $(".pricing-levels-3 input:checkbox:checked").length;
if (numberOfChecked >= 2) {
$(".pricing-levels-3 input:not(:checked)").prop("disabled", true);
} else {
$(".pricing-levels-3 input:not(:checked)").removeAttr("disabled", true);
}
});
});
})(jQuery);

This is working for me with checkbox name.
<script>
// limit checkbox select
$('input[name=vehicle]').on('change', function (e) {
if ($('input[name=vehicle]:checked').length > 3) {
$(this).prop('checked', false);
alert("allowed only 3");
}
});
</script>

This is how I made it work:
// Function to check and disable checkbox
function limit_checked( element, size ) {
var bol = $( element + ':checked').length >= size;
$(element).not(':checked').attr('disabled',bol);
}
// List of checkbox groups to check
var check_elements = [
{ id: '.group1 input[type=checkbox]', size: 2 },
{ id: '.group2 input[type=checkbox]', size: 3 },
];
// Run function for each group in list
$(check_elements).each( function(index, element) {
// Limit checked on window load
$(window).load( function() {
limit_checked( element.id, element.size );
})
// Limit checked on click
$(element.id).click(function() {
limit_checked( element.id, element.size );
});
});

I have Alter this function to auto uncheck previous
var limit = 3;
$('.compare_items').on('click', function(evt) {
index = $(this).parent('td').parent('tr').index();
if ($('.compare_items:checked').length >= limit) {
$('.compare_items').eq(localStorage.getItem('last-checked-item')).removeAttr('checked');
//this.checked = false;
}
localStorage.setItem('last-checked-item', index);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="checkbox" class="compare_items">1
<input type="checkbox" class="compare_items">2
<input type="checkbox" class="compare_items">3
<input type="checkbox" class="compare_items">4
<input type="checkbox" class="compare_items">5
<input type="checkbox" class="compare_items">6
<input type="checkbox" class="compare_items">7
<input type="checkbox" class="compare_items">8
<input type="checkbox" class="compare_items">9
<input type="checkbox" class="compare_items">10

I did this today, the difference being I wanted to uncheck the oldest checkbox instead of stopping the user from checking a new one:
let maxCheckedArray = [];
let assessmentOptions = jQuery('.checkbox-fields').find('input[type="checkbox"]');
assessmentOptions.on('change', function() {
let checked = jQuery(this).prop('checked');
if(checked) {
maxCheckedArray.push(jQuery(this));
}
if(maxCheckedArray.length >= 3) {
let old_item = maxCheckedArray.shift();
old_item.prop('checked', false);
}
});

This method works well with checkboxes in a container, such as bootstrap checkbox
const checkedLimmit = 2;
function ValidateCheckBoxGroup(container) {
if (container.find('input[type="checkbox"]:checked').length >= checkedLimmit) {
container.find('input[type="checkbox"]:not(:checked)').prop('disabled', true);
container.find('input[type="checkbox"]:not(:checked)').closest('div.checkbox').addClass('disabled');
} else {
container.find('input[type="checkbox"]:not(:checked)').prop('disabled', false);
container.find('input[type="checkbox"]:not(:checked)').closest('div.checkbox').removeClass('disabled');
}
}
$(function () {
// validate containers on page load
$('div.checkbox-group').each(function () {
ValidateCheckBoxGroup($(this));
});
// set checkbox events
$('div.checkbox-group input[type="checkbox"]').change(function () {
ValidateCheckBoxGroup($(this).closest("div.checkbox-group"));
});
});

JS and HTML
This worked for me what it does is that, the onclick function checkControl() will count the number of times the checkbox has been clicked then if it's greater than 3 display error message.
function checkboxControl(j) {
var total = 0;
var elem = document.getElementsByClassName("checkbox");
var error = document.getElementById("error");
for (var i = 0; i < elem.length; i++) {
if (elem[i].checked == true) {
total = total + 1;
}
if (total > 3) {
error.textContent = "You Must Select at Least 3";
elem[j].checked = false;
return false;
}
}
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
</head>
<body>
<form action="">
<span id="error" style="color: red"></span>
<br>
<span>Python</span>
<input
type="checkbox"
class="checkbox"
name="interest[]"
onclick="checkboxControl(0)"
id="1"
/>
<br>
<span>Javascript</span>
<input
type="checkbox"
class="checkbox"
name="interest[]"
onclick="checkboxControl(1)"
id="1"
/><br>
<span>Go</span>
<input
type="checkbox"
class="checkbox"
name="interest[]"
onclick="checkboxControl(2)"
id="1"
/><br>
<span>Laravel</span>
<input
type="checkbox"
class="checkbox"
name="interest[]"
onclick="checkboxControl(3)"
id="1"
/>
</form>
</body>
</html>
This resources helped me understand
https://www.plus2net.com/javascript_tutorial/checkbox-limit-demo2.php

If you want to uncheck the checkbox that you have selected first under the condition of 3 checkboxes allowed. With vanilla javascript; you need to assign onclick = "checking(this)" in your html input checkbox
var queue = [];
function checking(id){
queue.push(id)
if (queue.length===3){
queue[0].checked = false
queue.shift()
}
}

This function simply checks if you have just checked a checkbox. If yes, it increments the checked value by one. If it reaches the limit then the next checkbox is rejected.
var limit = 3;
var checked = 0;
$('.single-checkbox').on('change', function() {
if($(this).is(':checked'))
checked = checked+1;
if($(this).is(':checked') == false)
checked = checked-1;
if(checked > limit) {
this.checked = false;
checked = limit;
}
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="pricing-levels-3">
<p><strong>Which level would you like? (Select 3 Levels)</strong></p>
<input class="single-checkbox"type="checkbox" name="vehicle" value="Bike">Level 1<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 2<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 3<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 4<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 5<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 6<br>
<input class="single-checkbox" type="checkbox" name="vehicle" value="Bike">Level 7<br>
</div>

How to check uncheck checkboxes inside nested gridview using javascript or jquery

Actually, I implemented half of the code like if one checkbox is checked then check all checkboxes under that checkbox.
But now I want to uncheck the main checkbox if I marked uncheck on other checkboxes too...
please help me appropriate with this...
my code:
<script type="text/javascript">
function SelectAllCheckboxesA(chk, chk1, chk2, chk3, chk4) {
document.getElementById(chk1).checked = document.getElementById(chk2).checked = document.getElementById(chk3).checked = document.getElementById(chk4).checked = document.getElementById(chk).checked;
if (document.getElementById(chk1).checked == false || document.getElementById(chk2).checked == false || document.getElementById(chk3).checked == false || document.getElementById(chk4).checked == false) document.getElementById(chk).checked = false;
}
</script>

If you assign a css class to the parent check box and and another class for all the children it will be easier.
<html>
<body>
<br><br>
<input type="checkbox" class="parent" name="vehicle" > Parent<br>
<br>
<input type="checkbox" class="child" name="vehicle"> child 1<br>
<input type="checkbox" class="child" name="vehicle"> child 2<br>
<input type="checkbox" class="child" name="vehicle"> child 3<br>
<script type="text/javascript">
var parentCheckBox = document.querySelector(".parent");
var childCheckBoxes = document.querySelectorAll(".child");
parentCheckBox.onclick = function(){
childCheckBoxes.forEach(function(child){
child.checked=parentCheckBox.checked;
});
}
childCheckBoxes.forEach(function(child){
child.onclick = function(){
var allchecked = true;
childCheckBoxes.forEach(function(childBox){
allchecked = allchecked? childBox.checked : allchecked;
});
parentCheckBox.checked = allchecked;
}
});
</script>
</body>
</html>
Here is the demo https://jsfiddle.net/m23txgdz/

How to checked checkbox main when sub checkbox not checked?

How to checked checkbox main when sub checkbox not checked ?
When checkbox id="checkItem1" and id="checkItem2" and id="checkItem3" not checked,
i want to auto checked checkbox id="checkAll" how can i do that ?
http://jsfiddle.net/peap/sydzL8Lc/11/
<input type="checkbox" id="checkAll" checked > Check All
<hr />
<input type="checkbox" id="checkItem1"> Item 1
<input type="checkbox" id="checkItem2"> Item 2
<input type="checkbox" id="checkItem3"> Item3

you can do it like bellow
$('input[id^="checkItem"]').change(function(){
if($('input[id^="checkItem"]:checked').length===0)
$('#checkAll').prop('checked',true);
})
DEMO

I did a JSFiddle on the full functionality you will need including including when user click the checkAll all boxes change to checked if checkAll is checked or to not checked otherwise. Also there's a on change listener on each of them to listen if the user check all of them and to change the checkAll to checked and backwards.
HTML:
<input type="checkbox" id="checkAll"> Check All
<hr />
<div class='js-checkboxes'>
<input type="checkbox" id="checkItem1"> Item 1
<input type="checkbox" id="checkItem2"> Item 2
<input type="checkbox" id="checkItem3"> Item3
</div>
Javascript:
$('.js-checkboxes > input').on('change', function() {
var isAllChecked = true;
$('.js-checkboxes > input').each(function() {
if (!this.checked) {
isAllChecked = false;
}
});
if (isAllChecked) {
$('#checkAll')[0].checked = true;
} else {
$('#checkAll')[0].checked = false;
}
});
$('#checkAll').on('change', function() {
if (this.checked) {
$('.js-checkboxes > input').each(function() {
this.checked = true;
});
} else {
$('.js-checkboxes > input').each(function() {
this.checked = false;
});
}
});

$("input[id^='checkItem']").change(function(){
if(!$("#checkItem1").is(":checked") && !$("#checkItem2").is(":checked") && !$("#checkItem3").is(":checked"))
{
$("#checkAll").prop("checked",true)
}
}
EDIT :- DEMO

array of checkbox value checked and unchecked

I have this function, when I checked one or more checkbox the function load the value of the checked checkbox...but when I unchecked one or more check box the function show an empty array.
this is the function:
$(document).ready(function () {
$('input[type="checkbox"]').change(function () {
var mycheck = new Array();
if ($(this).is(':checked')) {
$("#line-checkbox-1:checked").each(function () {
mycheck.push($(this).val());//aggiungo value del checked
});
alert(mycheck)
} else {
var itemtoRemove = $(this);
mycheck.splice($.inArray(itemtoRemove, mycheck), 1); //rimuovo il value del dechecked
alert(mycheck);
}
});
This is HTML of the checkbox:
<div class="col-lg-3">
<input tabindex="17" id="line-checkbox-1" type="checkbox" name="servizi" value="3">
</div>

Try This Simple Script, this works for you:
HTML
<input type="checkbox" name="options[]" value="1" />
<input type="checkbox" name="options[]" value="2" />
<input type="checkbox" name="options[]" value="3" />
<input type="checkbox" name="options[]" value="4" />
<input type="checkbox" name="options[]" value="5" />
JQUERY
$(document).ready(function ()
{
$('input[type="checkbox"]').change(function ()
{
var arr = $.map($('input:checkbox:checked'), function(e,i) {
return +e.value;
});
alert(arr);
});
});

Its probably because you are using id to reference the checkboxes and since you are creating the array from scratch everytime user changes a checkbox. you should recheck the list everytime a checkbox is changed. That means you dont need that if.( if($(this).is(":checked") )
$('.checkboxes input[type="checkbox"]').change(function () {
var mycheck = new Array();
$(".checkboxes input[type='checkbox']:checked").each(function () {
if ($(this).is(':checked')) {
mycheck.push($(this).attr("id") + ": is " + $(this).val()); //aggiungo value del checked
}
});
alert(mycheck);
});
here is a fiddle if i understand correctly what you are trying to do

How to implement "select all" check box in HTML?

I have an HTML page with multiple checkboxes.
I need one more checkbox by the name "select all". When I select this checkbox all checkboxes in the HTML page must be selected. How can I do this?

<script language="JavaScript">
function toggle(source) {
checkboxes = document.getElementsByName('foo');
for(var checkbox in checkboxes)
checkbox.checked = source.checked;
}
</script>
<input type="checkbox" onClick="toggle(this)" /> Toggle All<br/>
<input type="checkbox" name="foo" value="bar1"> Bar 1<br/>
<input type="checkbox" name="foo" value="bar2"> Bar 2<br/>
<input type="checkbox" name="foo" value="bar3"> Bar 3<br/>
<input type="checkbox" name="foo" value="bar4"> Bar 4<br/>
UPDATE:
The for each...in construct doesn't seem to work, at least in this case, in Safari 5 or Chrome 5. This code should work in all browsers:
function toggle(source) {
checkboxes = document.getElementsByName('foo');
for(var i=0, n=checkboxes.length;i<n;i++) {
checkboxes[i].checked = source.checked;
}
}

Using jQuery:
// Listen for click on toggle checkbox
$('#select-all').click(function(event) {
if(this.checked) {
// Iterate each checkbox
$(':checkbox').each(function() {
this.checked = true;
});
} else {
$(':checkbox').each(function() {
this.checked = false;
});
}
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<input type="checkbox" name="checkbox-1" id="checkbox-1" />
<input type="checkbox" name="checkbox-2" id="checkbox-2" />
<input type="checkbox" name="checkbox-3" id="checkbox-3" />
<!-- select all boxes -->
<input type="checkbox" name="select-all" id="select-all" />

I'm not sure anyone hasn't answered in this way (using jQuery):
$( '#container .toggle-button' ).click( function () {
$( '#container input[type="checkbox"]' ).prop('checked', this.checked)
})
It's clean, has no loops or if/else clauses and works as a charm.

I'm surprised no one mentioned document.querySelectorAll(). Pure JavaScript solution, works in IE9+.
function toggle(source) {
var checkboxes = document.querySelectorAll('input[type="checkbox"]');
for (var i = 0; i < checkboxes.length; i++) {
if (checkboxes[i] != source)
checkboxes[i].checked = source.checked;
}
}
<input type="checkbox" onclick="toggle(this);" />Check all?<br />
<input type="checkbox" />Bar 1<br />
<input type="checkbox" />Bar 2<br />
<input type="checkbox" />Bar 3<br />
<input type="checkbox" />Bar 4<br />

here's a different way less code
$(function () {
$('#select-all').click(function (event) {
var selected = this.checked;
// Iterate each checkbox
$(':checkbox').each(function () { this.checked = selected; });
});
});

Demo http://jsfiddle.net/H37cb/
<script type="text/javascript" src="http://code.jquery.com/jquery-latest.min.js" /></script>
<script type="text/javascript">
$(document).ready(function(){
$('input[name="all"],input[name="title"]').bind('click', function(){
var status = $(this).is(':checked');
$('input[type="checkbox"]', $(this).parent('li')).attr('checked', status);
});
});
</script>
<div id="wrapper">
<li style="margin-top: 20px">
<input type="checkbox" name="all" id="all" /> <label for='all'>All</label>
<ul>
<li><input type="checkbox" name="title" id="title_1" /> <label for="title_1"><strong>Title 01</strong></label>
<ul>
<li><input type="checkbox" name="selected[]" id="box_1" value="1" /> <label for="box_1">Sub Title 01</label></li>
<li><input type="checkbox" name="selected[]" id="box_2" value="2" /> <label for="box_2">Sub Title 02</label></li>
<li><input type="checkbox" name="selected[]" id="box_3" value="3" /> <label for="box_3">Sub Title 03</label></li>
<li><input type="checkbox" name="selected[]" id="box_4" value="4" /> <label for="box_4">Sub Title 04</label></li>
</ul>
</li>
</ul>
<ul>
<li><input type="checkbox" name="title" id="title_2" /> <label for="title_2"><strong>Title 02</strong></label>
<ul>
<li><input type="checkbox" name="selected[]" id="box_5" value="5" /> <label for="box_5">Sub Title 05</label></li>
<li><input type="checkbox" name="selected[]" id="box_6" value="6" /> <label for="box_6">Sub Title 06</label></li>
<li><input type="checkbox" name="selected[]" id="box_7" value="7" /> <label for="box_7">Sub Title 07</label></li>
</ul>
</li>
</ul>
</li>
</div>

When you call document.getElementsByName("name"), you will get a Object. Use .item(index) to traverse all items of a Object
HTML:
<input type="checkbox" onclick="for(c in document.getElementsByName('rfile')) document.getElementsByName('rfile').item(c).checked = this.checked">
<input type=​"checkbox" name=​"rfile" value=​"/​cgi-bin/​">​
<input type=​"checkbox" name=​"rfile" value=​"/​includes/​">​
<input type=​"checkbox" name=​"rfile" value=​"/​misc/​">​
<input type=​"checkbox" name=​"rfile" value=​"/​modules/​">​
<input type=​"checkbox" name=​"rfile" value=​"/​profiles/​">​
<input type=​"checkbox" name=​"rfile" value=​"/​scripts/​">​
<input type=​"checkbox" name=​"rfile" value=​"/​sites/​">​
<input type=​"checkbox" name=​"rfile" value=​"/​stats/​">​
<input type=​"checkbox" name=​"rfile" value=​"/​themes/​">​

Slightly changed version which checks and unchecks respectfully
$('#select-all').click(function(event) {
var $that = $(this);
$(':checkbox').each(function() {
this.checked = $that.is(':checked');
});
});

My simple solution allows to selectively select/deselect all checkboxes in a given portion of the form, while using different names for each checkbox, so that they can be easily recognized after the form is POSTed.
Javascript:
function setAllCheckboxes(divId, sourceCheckbox) {
divElement = document.getElementById(divId);
inputElements = divElement.getElementsByTagName('input');
for (i = 0; i < inputElements.length; i++) {
if (inputElements[i].type != 'checkbox')
continue;
inputElements[i].checked = sourceCheckbox.checked;
}
}
HTML example:
<p><input onClick="setAllCheckboxes('actors', this);" type="checkbox" />All of them</p>
<div id="actors">
<p><input type="checkbox" name="kevin" />Spacey, Kevin</p>
<p><input type="checkbox" name="colin" />Firth, Colin</p>
<p><input type="checkbox" name="scarlett" />Johansson, Scarlett</p>
</div>
I hope you like it!

<html>
<head>
<script type="text/javascript">
function do_this(){
var checkboxes = document.getElementsByName('approve[]');
var button = document.getElementById('toggle');
if(button.value == 'select'){
for (var i in checkboxes){
checkboxes[i].checked = 'FALSE';
}
button.value = 'deselect'
}else{
for (var i in checkboxes){
checkboxes[i].checked = '';
}
button.value = 'select';
}
}
</script>
</head>
<body>
<input type="checkbox" name="approve[]" value="1" />
<input type="checkbox" name="approve[]" value="2" />
<input type="checkbox" name="approve[]" value="3" />
<input type="button" id="toggle" value="select" onClick="do_this()" />
</body>
</html>

Try this simple JQuery:
$('#select-all').click(function(event) {
if (this.checked) {
$(':checkbox').prop('checked', true);
} else {
$(':checkbox').prop('checked', false);
}
});

JavaScript is your best bet. The link below gives an example using buttons to de/select all. You could try to adapt it to use a check box, just use you 'select all' check box' onClick attribute.
Javascript Function to Check or Uncheck all Checkboxes
This page has a simpler example
http://www.htmlcodetutorial.com/forms/_INPUT_onClick.html

This sample works with native JavaScript where the checkbox variable name varies, i.e. not all "foo."
<!DOCTYPE html>
<html>
<body>
<p>Toggling checkboxes</p>
<script>
function getcheckboxes() {
var node_list = document.getElementsByTagName('input');
var checkboxes = [];
for (var i = 0; i < node_list.length; i++)
{
var node = node_list[i];
if (node.getAttribute('type') == 'checkbox')
{
checkboxes.push(node);
}
}
return checkboxes;
}
function toggle(source) {
checkboxes = getcheckboxes();
for (var i = 0 n = checkboxes.length; i < n; i++)
{
checkboxes[i].checked = source.checked;
}
}
</script>
<input type="checkbox" name="foo1" value="bar1"> Bar 1<br/>
<input type="checkbox" name="foo2" value="bar2"> Bar 2<br/>
<input type="checkbox" name="foo3" value="bar3"> Bar 3<br/>
<input type="checkbox" name="foo4" value="bar4"> Bar 4<br/>
<input type="checkbox" onClick="toggle(this)" /> Toggle All<br/>
</body>
</html>

It's rather simple:
const selectAllCheckboxes = () => {
const checkboxes = document.querySelectorAll('input[type=checkbox]');
checkboxes.forEach((cb) => { cb.checked = true; });
}

If adopting the top answer for jQuery, remember that the object passed to the click function is an EventHandler, not the original checkbox object. Therefore code should be modified as follows.
HTML
<input type="checkbox" name="selectThemAll"/> Toggle All<br/>
<input type="checkbox" name="foo" value="bar1"> Bar 1<br/>
<input type="checkbox" name="foo" value="bar2"> Bar 2<br/>
<input type="checkbox" name="foo" value="bar3"> Bar 3<br/>
<input type="checkbox" name="foo" value="bar4"> Bar 4<br/>
Javascript
$(function() {
jQuery("[name=selectThemAll]").click(function(source) {
checkboxes = jQuery("[name=foo]");
for(var i in checkboxes){
checkboxes[i].checked = source.target.checked;
}
});
})

<asp:CheckBox ID="CheckBox1" runat="server" Text="Select All" onclick="checkAll(this);" />
<br />
<asp:CheckBoxList ID="CheckBoxList1" runat="server">
<asp:ListItem Value="Item 1">Item 1</asp:ListItem>
<asp:ListItem Value="Item 2">Item 2</asp:ListItem>
<asp:ListItem Value="Item 3">Item 3</asp:ListItem>
<asp:ListItem Value="Item 4">Item 4</asp:ListItem>
<asp:ListItem Value="Item 5">Item 5</asp:ListItem>
<asp:ListItem Value="Item 6">Item 6</asp:ListItem>
</asp:CheckBoxList>
<script type="text/javascript">
function checkAll(obj1) {
var checkboxCollection = document.getElementById('<%=CheckBoxList1.ClientID %>').getElementsByTagName('input');
for (var i = 0; i < checkboxCollection.length; i++) {
if (checkboxCollection[i].type.toString().toLowerCase() == "checkbox") {
checkboxCollection[i].checked = obj1.checked;
}
}
}
</script>

that should do the job done:
$(':checkbox').each(function() {
this.checked = true;
});

You may have different sets of checkboxes on the same form. Here is a solution that selects/unselects checkboxes by class name, using vanilla javascript function document.getElementsByClassName
The Select All button
<input type='checkbox' id='select_all_invoices' onclick="selectAll()"> Select All
Some of the checkboxes to select
<input type='checkbox' class='check_invoice' id='check_123' name='check_123' value='321' />
<input type='checkbox' class='check_invoice' id='check_456' name='check_456' value='852' />
The javascript
function selectAll() {
var blnChecked = document.getElementById("select_all_invoices").checked;
var check_invoices = document.getElementsByClassName("check_invoice");
var intLength = check_invoices.length;
for(var i = 0; i < intLength; i++) {
var check_invoice = check_invoices[i];
check_invoice.checked = blnChecked;
}
}

This is what this will do, for instance if you have 5 checkboxes, and you click check all,it check all, now if you uncheck all the checkbox probably by clicking each 5 checkboxs, by the time you uncheck the last checkbox, the select all checkbox also gets unchecked
$("#select-all").change(function(){
$(".allcheckbox").prop("checked", $(this).prop("checked"))
})
$(".allcheckbox").change(function(){
if($(this).prop("checked") == false){
$("#select-all").prop("checked", false)
}
if($(".allcheckbox:checked").length == $(".allcheckbox").length){
$("#select-all").prop("checked", true)
}
})

As I cannot comment, here as answer:
I would write Can Berk Güder's solution in a more general way,
so you may reuse the function for other checkboxes
<script language="JavaScript">
function toggleCheckboxes(source, cbName) {
checkboxes = document.getElementsByName(cbName);
for (var i = 0, n = checkboxes.length; i < n; i++) {
checkboxes[i].checked = source.checked;
}
}
</script>
<input type="checkbox" onClick="toggleCheckboxes(this,\'foo\')" /> Toggle All<br/>
<input type="checkbox" name="foo" value="bar1"> Bar 1<br/>
<input type="checkbox" name="foo" value="bar2"> Bar 2<br/>
<input type="checkbox" name="foo" value="bar3"> Bar 3<br/>
<input type="checkbox" name="foo" value="bar4"> Bar 4<br/>
<input type="checkbox" name="foo" value="bar5"> Bar 5<br/>

$(document).ready(function() {
$(document).on(' change', 'input[name="check_all"]', function() {
$('.cb').prop("checked", this.checked);
});
});

Using jQuery and knockout:
With this binding main checkbox stays in sync with underliying checkboxes, it will be unchecked unless all checkboxes checked.
ko.bindingHandlers.allChecked = {
init: function (element, valueAccessor) {
var selector = valueAccessor();
function getChecked () {
element.checked = $(selector).toArray().every(function (checkbox) {
return checkbox.checked;
});
}
function setChecked (value) {
$(selector).toArray().forEach(function (checkbox) {
if (checkbox.checked !== value) {
checkbox.click();
}
});
}
ko.utils.registerEventHandler(element, 'click', function (event) {
setChecked(event.target.checked);
});
$(window.document).on('change', selector, getChecked);
ko.utils.domNodeDisposal.addDisposeCallback(element, () => {
$(window.document).off('change', selector, getChecked);
});
getChecked();
}
};
in html:
<input id="check-all-values" type="checkbox" data-bind="allChecked: '.checkValue'"/>
<input id="check-1" type="checkbox" class="checkValue"/>
<input id="check-2" type="checkbox" class="checkValue"/>

to make it in short-hand version by using jQuery
The select all checkbox
<input type="checkbox" id="chkSelectAll">
The children checkbox
<input type="checkbox" class="chkDel">
<input type="checkbox" class="chkDel">
<input type="checkbox" class="chkDel">
jQuery
$("#chkSelectAll").on('click', function(){
this.checked ? $(".chkDel").prop("checked",true) : $(".chkDel").prop("checked",false);
})

Below methods are very Easy to understand and you can implement existing forms in minutes
With Jquery,
$(document).ready(function() {
$('#check-all').click(function(){
$("input:checkbox").attr('checked', true);
});
$('#uncheck-all').click(function(){
$("input:checkbox").attr('checked', false);
});
});
in HTML form put below buttons
<a id="check-all" href="javascript:void(0);">check all</a>
<a id="uncheck-all" href="javascript:void(0);">uncheck all</a>
With just using javascript,
<script type="text/javascript">
function checkAll(formname, checktoggle)
{
var checkboxes = new Array();
checkboxes = document[formname].getElementsByTagName('input');
for (var i=0; i<checkboxes.length; i++) {
if (checkboxes[i].type == 'checkbox') {
checkboxes[i].checked = checktoggle;
}
}
}
</script>
in HTML form put below buttons
<button onclick="javascript:checkAll('form3', true);" href="javascript:void();">check all</button>
<button onclick="javascript:checkAll('form3', false);" href="javascript:void();">uncheck all</button>

Here is a backbone.js implementation:
events: {
"click #toggleChecked" : "toggleChecked"
},
toggleChecked: function(event) {
var checkboxes = document.getElementsByName('options');
for(var i=0; i<checkboxes.length; i++) {
checkboxes[i].checked = event.currentTarget.checked;
}
},

html
<input class='all' type='checkbox'> All
<input class='item' type='checkbox' value='1'> 1
<input class='item' type='checkbox' value='2'> 2
<input class='item' type='checkbox' value='3'> 3
javascript
$(':checkbox.all').change(function(){
$(':checkbox.item').prop('checked', this.checked);
});

1: Add the onchange event Handler
<th><INPUT type="checkbox" onchange="checkAll(this)" name="chk[]" /> </th>
2: Modify the code to handle checked/unchecked
function checkAll(ele) {
var checkboxes = document.getElementsByTagName('input');
if (ele.checked) {
for (var i = 0; i < checkboxes.length; i++) {
if (checkboxes[i].type == 'checkbox') {
checkboxes[i].checked = true;
}
}
} else {
for (var i = 0; i < checkboxes.length; i++) {
console.log(i)
if (checkboxes[i].type == 'checkbox') {
checkboxes[i].checked = false;
}
}
}
}

You can Use This code.
var checkbox = document.getElementById("dlCheckAll4Delete");
checkbox.addEventListener("click", function (event) {
let checkboxes = document.querySelectorAll(".dlMultiDelete");
checkboxes.forEach(function (ele) {
ele.checked = !!checkbox.checked;
});
});

You can use this simple code
$('.checkall').click(function(){
var checked = $(this).prop('checked');
$('.checkme').prop('checked', checked);
});

Maybe a bit late, but when dealing with a check all checkbox, I believe you should also handle the scenario for when you have the check all checkbox checked, and then unchecking one of the checkboxes below.
In that case it should automatically uncheck the check all checkbox.
Also when manually checking all the checkboxes, you should end up with the check all checkbox being automatically checked.
You need two event handlers, one for the check all box, and one for when clicking any of the single boxes below.
// HANDLES THE INDIVIDUAL CHECKBOX CLICKS
function client_onclick() {
var selectAllChecked = $("#chk-clients-all").prop("checked");
// IF CHECK ALL IS CHECKED, AND YOU'RE UNCHECKING AN INDIVIDUAL BOX, JUST UNCHECK THE CHECK ALL CHECKBOX.
if (selectAllChecked && $(this).prop("checked") == false) {
$("#chk-clients-all").prop("checked", false);
} else { // OTHERWISE WE NEED TO LOOP THROUGH INDIVIDUAL CHECKBOXES AND SEE IF THEY ARE ALL CHECKED, THEN CHECK THE SELECT ALL CHECKBOX ACCORDINGLY.
var allChecked = true;
$(".client").each(function () {
allChecked = $(this).prop("checked");
if (!allChecked) {
return false;
}
});
$("#chk-clients-all").prop("checked", allChecked);
}
}
// HANDLES THE TOP CHECK ALL CHECKBOX
function client_all_onclick() {
$(".client").prop("checked", $(this).prop("checked"));
}