// The jQuery.fn.extend() method extends the jQuery prototype ($.fn)
// object to provide new methods that can be chained
// to the jQuery() function.
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>jQuery.fn.extend demo</title>
<style>
label {
display: block;
margin: .5em;
}
</style>
<script src="https://code.jquery.com/jquery-3.5.0.js"></script>
</head>
<body>
<label><input type="checkbox" name="foo"> Foo</label>
<label><input type="checkbox" name="bar"> Bar</label>
<script>
jQuery.fn.extend({
check: function() {
return this.each(function() {
this.checked = true;
});
},
uncheck: function() {
return this.each(function() {
this.checked = false;
});
}
});
// Use the newly created .check() method
$( "input[type='checkbox']" ).check();
</script>
</body>
</html>