How to check or uncheck checkbox using jQuery?

jQuery prop() method can be used to check or uncheck a checkbox dynamically

The prop() method require jQuery 1.6 and above, here is the sample

$('#YouCheckboxId').prop('checked', true); // Check
$('#YouCheckboxId').prop('checked', false); // Uncheck, may not work in some browsers

$('#YouCheckboxId').removeAttr('checked'); //uncheck, by removing attribute

Below jQuery 1.6 you can use .attr()

$('#YouCheckboxId').attr('checked', true); // Check 
$('#YouCheckboxId').attr('checked', false); // Uncheck

Note: An element is considered checked as long as it has the attribute of checked even if it has no value or the value is like 'false' or whatever, so to uncheck the checkbox, it is safe to use attribute removeAttr("checked").

You can have custom function like below for check using

$('.myCheckbox').attr('checked',true)

and uncheck using 

$('.myCheckbox').removeAttr('checked')

For jQuery 1.6 + use .prop

$('.myCheckbox').prop('checked', true); // Checks it
$('.myCheckbox').prop('checked', false); // Unchecks it

Plain Javascript, using ClassName

var elements = document.getElementsByClassName('myCheckBox');
for(var i = 0; i < elements.length; i++)
{
    elements[i].checked = true;
}

Make it 'false' to unchecking checkbox.