check / uncheck checkbox using jquery?

For jQuery 1.6+ :

.attr() is deprecated for properties; use the new .prop() function instead as:

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

For jQuery < 1.6:

To check/uncheck a checkbox, use the attribute checked and alter that. With jQuery you can do:

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

Cause you know, in HTML, it would look something like:

<input type="checkbox" id="myCheckbox" checked="checked" /> <!-- Checked -->
<input type="checkbox" id="myCheckbox" /> <!-- Unchecked -->

However, you cannot trust the .attr() method to get the value of the checkbox (if you need to). You will have to rely in the .prop() method.

You can use prop() for this, as Before jQuery 1.6, the .attr() method sometimes took property values into account when retrieving some attributes, which could cause inconsistent behavior. As of jQuery 1.6, the .prop() method provides a way to explicitly retrieve property values, while .attr() retrieves attributes.

var prop=false;
if(value == 1) {
   prop=true; 
}
$('#checkbox').prop('checked',prop);

or simply,

$('#checkbox').prop('checked',(value == 1));

Snippet

$(document).ready(function() {
  var chkbox = $('.customcheckbox');
  $(".customvalue").keyup(function() {
    chkbox.prop('checked', this.value==1);
  });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<h4>This is a domo to show check box is checked
if you enter value 1 else check box will be unchecked </h4>
Enter a value:
<input type="text" value="" class="customvalue">
<br>checkbox output :
<input type="checkbox" class="customcheckbox">

You can set the state of the checkbox based on the value:

$('#your-checkbox').prop('checked', value == 1);