jquery - 如果延迟已经解决，jquery 延迟回调是否同步？

Question

我猜答案是肯定的，但代码并不是最容易破译的。并在 docs它说

Any callbacks added to the object with deferred.then(), deferred.always(), deferred.done(), or deferred.fail() are queued to be executed later. Calling deferred.resolve() or deferred.resolveWith() transitions the Deferred into the resolved state and immediately executes any doneCallbacks that are set.

但这并没有明确涵盖将回调附加到已解析的 Deferred 的情况。

Answer 1

如果 promise 已经解决/拒绝，则新的回调将同步执行。

来自jQuery.deferred() doc :

Once the object has entered the resolved or rejected state, it stays in that state. Callbacks can still be added to the resolved or rejected Deferred — they will execute immediately.

演示 (Fiddle):

var def = jQuery.Deferred(),
    promise = def.promise();
console.log('before 1');
promise.done(function () {
    console.log('done 1');
});
console.log('after 1');
def.resolve();
console.log('before 2');
promise.done(function () {
    console.log('done 2');
});
console.log('after 2');

输出:

before 1
after 1
done 1
before 2
done 2
after 2