jQuery中首先出现的.always()或.then()回调是什么?

问题描述：

如果您的函数同时具有.then和.always回调，哪个将首先执行?

If you have a function which has both .then and .always callbacks, which one will get executed first?

答

来自 deferred.resolve() 文档:

延迟解决后，任何由添加的doneCallbacks deferred.then()或deferred.done()会被调用.执行回调按照它们的添加顺序.

When the Deferred is resolved, any doneCallbacks added by deferred.then() or deferred.done() are called. Callbacks are executed in the order they were added.

以下示例:

var $logger = $("#logEntry");
function addLog(content){
   $logger.append($("<li/>").html(content));
}

var newPromise = $.Deferred();

$.when(newPromise).done(function() {
    addLog("1st $when().done!");
});

newPromise.then(function() {
    addLog("1st then!");
}).always(function() {
    addLog("1st always!");
}).done(function() {
    addLog("1st done!");
}).done(function() {
    addLog("2nd done!");
}).always(function() {
    addLog("2nd always!");
}).then(function() {
    addLog("2nd then!");
});

$.when(newPromise).done(function() {
    addLog("2nd $when().done!");
});

addLog("Resolving promise!");

newPromise.resolve();

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<ul id="logEntry"></ul>

jQuery中首先出现的.always()或.then()回调是什么?

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