How to check all checkboxes using jQuery?

You need to use .prop() to set the checked property

$("#checkAll").click(function(){
    $('input:checkbox').not(this).prop('checked', this.checked);
});

Demo: Fiddle

Simply use the checked property of the checkAll and use use prop() instead of attr for checked property

Live Demo

 $('#checkAll').click(function () {    
     $('input:checkbox').prop('checked', this.checked);    
 });

Use prop() instead of attr() for properties like checked

As of jQuery 1.6, the .attr() method returns undefined for attributes that have not been set. To retrieve and change DOM properties such as the checked, selected, or disabled state of form elements, use the .prop() method

You have same id for checkboxes and its should be unique. You better use some class with the dependent checkboxes so that it does not include the checkboxes you do not want. As $('input:checkbox') will select all checkboxes on the page. If your page is extended with new checkboxes then they will also get selected/un-selected. Which might not be the intended behaviour.

Live Demo

$('#checkAll').click(function () {    
    $(':checkbox.checkItem').prop('checked', this.checked);    
});

A complete solution is here.

$(document).ready(function() {
    $("#checkedAll").change(function() {
        if (this.checked) {
            $(".checkSingle").each(function() {
                this.checked=true;
            });
        } else {
            $(".checkSingle").each(function() {
                this.checked=false;
            });
        }
    });

    $(".checkSingle").click(function () {
        if ($(this).is(":checked")) {
            var isAllChecked = 0;

            $(".checkSingle").each(function() {
                if (!this.checked)
                    isAllChecked = 1;
            });

            if (isAllChecked == 0) {
                $("#checkedAll").prop("checked", true);
            }     
        }
        else {
            $("#checkedAll").prop("checked", false);
        }
    });
});

Html should be :

Single check box on checked three checkbox will be select and deselect.

<input type="checkbox" name="checkedAll" id="checkedAll" />

<input type="checkbox" name="checkAll" class="checkSingle" />
<input type="checkbox" name="checkAll" class="checkSingle" />
<input type="checkbox" name="checkAll" class="checkSingle" />

Hope this helps to someone as it did for me.

JS Fiddle https://jsfiddle.net/52uny55w/

I think when user select all checkbox manually then checkall should be checked automatically or user unchecked one of them from all selected checkbox then checkall should be unchecked automically. here is my code..

$('#checkall').change(function () {
    $('.cb-element').prop('checked',this.checked);
});

$('.cb-element').change(function () {
 if ($('.cb-element:checked').length == $('.cb-element').length){
  $('#checkall').prop('checked',true);
 }
 else {
  $('#checkall').prop('checked',false);
 }
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<input type="checkbox" name="all" id="checkall" />Check All</br>
<input type="checkbox" class="cb-element" /> Checkbox  1</br>
<input type="checkbox" class="cb-element" /> Checkbox  2</br>
<input type="checkbox" class="cb-element" /> Checkbox  3

$(document).ready(function() {
  $("#parent").click(function() {
    $(".child").prop("checked", this.checked);
  });

  $('.child').click(function() {
    if ($('.child:checked').length == $('.child').length) {
      $('#parent').prop('checked', true);
    } else {
      $('#parent').prop('checked', false);
    }
  });
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
<p><input type="checkbox" id="parent" /> Check/Uncheck All</p>
<ul>
  <li>
    <input type="checkbox" class="child" /> Checkbox 1</li>
  <li>
    <input type="checkbox" class="child" /> Checkbox 2</li>
  <li>
    <input type="checkbox" class="child" /> Checkbox 3</li>
</ul>

HTML:

<p><input type="checkbox" id="parent" /> Check/Uncheck All</p>
<ul>
  <li>
    <input type="checkbox" class="child" /> Checkbox 1</li>
  <li>
    <input type="checkbox" class="child" /> Checkbox 2</li>
  <li>
    <input type="checkbox" class="child" /> Checkbox 3</li>
</ul>

jQuery:

$(document).ready(function() {
  $("#parent").click(function() {
    $(".child").prop("checked", this.checked);
  });

  $('.child').click(function() {
    if ($('.child:checked').length == $('.child').length) {
      $('#parent').prop('checked', true);
    } else {
      $('#parent').prop('checked', false);
    }
  });
});