How do I check whether a checkbox is checked in jQuery?

Question

How do I successfully query the checked property?

The checked property of a checkbox DOM element will give you the checked state of the element.

Given your existing code, you could therefore do this:

if(document.getElementById('isAgeSelected').checked) {
    $("#txtAge").show();
} else {
    $("#txtAge").hide();
}

However, there's a much prettier way to do this, using toggle:

$('#isAgeSelected').click(function() {
    $("#txtAge").toggle(this.checked);
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="checkbox" id="isAgeSelected"/>
<div id="txtAge" style="display:none">Age is something</div>

Use jQuery's is() function:

if($("#isAgeSelected").is(':checked'))
    $("#txtAge").show();  // checked
else
    $("#txtAge").hide();  // unchecked

Using jQuery > 1.6

<input type="checkbox" value="1" name="checkMeOut" id="checkMeOut" checked="checked" />

// traditional attr
$('#checkMeOut').attr('checked'); // "checked"
// new property method
$('#checkMeOut').prop('checked'); // true

Using the new property method:

if($('#checkMeOut').prop('checked')) {
    // something when checked
} else {
    // something else when not
}

jQuery 1.6+

$('#isAgeSelected').prop('checked')

jQuery 1.5 and below

$('#isAgeSelected').attr('checked')

Any version of jQuery

// Assuming an event handler on a checkbox
if (this.checked)

All credit goes to Xian.

I am using this and this is working absolutely fine:

$("#checkkBoxId").attr("checked") ? alert("Checked") : alert("Unchecked");

Note: If the checkbox is checked it will return true otherwise undefined, so better check for the "TRUE" value.

Use:

<input type="checkbox" name="planned_checked" checked id="planned_checked"> Planned

$("#planned_checked").change(function() {
    if($(this).prop('checked')) {
        alert("Checked Box Selected");
    } else {
        alert("Checked Box deselect");
    }
});

    $("#planned_checked").change(function() {
        if($(this).prop('checked')) {
            alert("Checked Box Selected");
        } else {
            alert("Checked Box deselect");
        }
    });

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<input type="checkbox" name="planned_checked" checked id="planned_checked"> Planned