filter() narrows a set to elements matching a selector or callback. not() removes matching elements. is() returns true or false — useful in conditionals like if ($(this).is('.active')) inside event handlers.
Filtering and Mapping
// Filter elements
$('li').filter('.active'); // by selector
$('li').filter(function() {
return $(this).text().length > 5;
});
// Map elements to array
const texts = $('li').map(function() {
return $(this).text();
}).get();
// not() — exclude elements
$('li').not('.done').css('color', 'blue');