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jQuery:checked Selector

Description: Matches all elements that are checked or selected.

version added: 1.0jQuery( ":checked" )

The :checked selector works for checkboxes, radio buttons, and options of select elements.

To retrieve only the selected options of select elements, use the :selected selector.

Examples:

Determine how many input elements are checked.

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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>checked demo</title>
<style>
div {
color: red;
}
</style>
<script src="https://code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
<form>
<p>
<input type="checkbox" name="newsletter" value="Hourly" checked="checked">
<input type="checkbox" name="newsletter" value="Daily">
<input type="checkbox" name="newsletter" value="Weekly">
<input type="checkbox" name="newsletter" value="Monthly" checked>
<input type="checkbox" name="newsletter" value="Yearly">
</p>
</form>
<div></div>
<script>
var countChecked = function() {
var n = $( "input:checked" ).length;
$( "div" ).text( n + (n === 1 ? " is" : " are") + " checked!" );
};
countChecked();
$( "input[type=checkbox]" ).on( "click", countChecked );
</script>
</body>
</html>

 

Identify the checked radio input.

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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>checked demo</title>
<style>
input, label {
line-height: 1.5em;
}
</style>
<script src="https://code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
<form>
<div>
<input type="radio" name="fruit" value="orange" id="orange">
<label for="orange">orange</label>
</div>
<div>
<input type="radio" name="fruit" value="apple" id="apple">
<label for="apple">apple</label>
</div>
<div>
<input type="radio" name="fruit" value="banana" id="banana">
<label for="banana">banana</label>
</div>
<div id="log"></div>
</form>
<script>
$( "input" ).on( "click", function() {
$( "#log" ).html( $( "input:checked" ).val() + " is checked!" );
});
</script>
</body>
</html>

from:http://api.jquery.com/checked-selector/