jQuery 延迟的优点？

Question

 $.ajax("example.php").done(function ()
 {
     alert(...);
 }).fail(function ()
 {
     alert(...);
 }).always(function ()
 {
      alert(...);
 });

对比

  $.ajax("example.php",

      success: function ()
      {
          alert('');
      },
      error: function ()
      {
          alert('');
      },
      complete: function ()
      {
          alert('');
      }
  );

抱歉，我看不到有什么优势

能解释一下吗？

或者也许你可以给我举个例子，前者无法通过后者完成......？

Answer 1

对于初学者来说，第二个代码块在语法上甚至无效。我认为这是第一个 :P

的优点<小时/>

但严肃地说:

这只是实现相同最终结果的不同语法。一个直接的好处是，您可以使用延迟为每个结果连接多个函数:

$.get("example.php").done(function ()
{
    alert("success 1");
}).done(function ()
{
    alert("success 2");
});

否则你必须这样做:

function done1()
{
    alert('success 1');
}
function done2()
{
    alert('success 2');
}

$.ajax('example.php',
{
    success: function ()
    {
        done1.apply(this, arguments);
        done2.apply(this, arguments);
    }
});

<小时/>

其他优点，引自How can jQuery deferred be used?

• Deferreds are perfect for when the task may or may not operate asynchronously, and you want to abstract that condition out of the code.
• ...Fetching data from multiple sources. In the example below, I'm fetching multiple, independent JSON schema objects used in an existing application for validation between a client and a REST server. In this case, I don't want the browser-side application to start loading data before it has all the schemas loaded. $.when.apply().then() is perfect for this.
• A deferred can be used in place of a mutex. This is essentially the same as the multiple ajax usage scenarios.