Deferred Summary
Key concepts: $.Deferred() creates a deferred, .resolve()/.reject() settles it, .done()/.fail()/.always() attach callbacks, $.when() combines multiple, .then() chains them.
jQuery
Beginner
3 min read
jQuery Deferred — Summary
Example
// Deferred cheatsheet
const dfd = $.Deferred();
dfd.resolve(value); // resolve
dfd.reject(reason); // reject
dfd.notify(progress); // progress
dfd.promise(); // read-only view
dfd.state(); // "pending"/"resolved"/"rejected"
jqXHR.done(fn).fail(fn).always(fn); // AJAX callbacks
$.when(p1, p2).done(fn); // parallel
p.then(success, failure); // chain + transform Pro Tip
In modern jQuery projects, use async/await with native Promises — Deferred is for legacy compatibility.