$.ajax({ success: function() { 
  $.ajax({ success: function() {
    $.ajax({ //callbacks... 
        }); 
  }); 
});  

var promises = []; 
$.ajax({
  success: function() { 
    promises.push('resolved'); 
    check(); 
  } 
}); 
$.ajax({ 
  success: function() { 
    promises.push('resolved'); 
    check();
  } 
}); 
$.ajax({ 
  success: function() { 
    promises.push('resolved'); 
    check(); 
  } 
}); 
var check = function() { //checks for all 3 values in the promises array }

var address = $.ajax({}); 
var tweets = $.ajax({}); 
var facebook = $.ajax({}); 
render_side_bar = function(address, tweets, facebook){ 
  //render sidebar 
}
render_no_side_bar = function () { }
$.when(address, tweets, facebook).then(render_side_bar, render_no_side_bar)

$.ajax("test.html")
　　.done(function(){ alert("first success callback!");} )
　　.fail(function(){ alert("there is an error!"); } )
　　.done(function(){ alert("second success callback!");} );

$.when($.ajax({}), $.ajax({}))
　　.done(function(){ alert("success!"); })
　　.fail(function(){ alert("error!"); });

var dfd = $.Deferred(); // create a deferred object
　　var wait = function(dtd){
　　　　var tasks = function(){
　　　　　　alert("over!");
　　　　　　dtd.resolve(); // change the state of the deferred object from pending to resolved
　　　　};
　　　　setTimeout(tasks,50000);
　　　　return dtd;
　　};

$.when(wait(dtd))
　　.done(function(){ alert("success!"); })
　　.fail(function(){ alert("error!"); });

$.ajax({
  url: "",
　　 success: function(){
　　　　alert("success!");
　　　},
　　　error:function(){
　　　　alert("error!");
　　　}
});

$.ajax({})
　　.done(function(){ alert("success!"); })
　　.fail(function(){ alert("fail!"); });

$.Deferred().state(); // 'pending'
$.Deferred().resolve().state(); // 'resolved'
$.Deferred().reject().state(); // 'rejected'

var callbackFunc = function(){console.log(arguments[0]);}
var dfd = $.Deferred();
dfd.done(callbackFunc);
dfd.resolve("hello"); //'hello'

var callbackFunc = function(){console.log(arguments[0]);}
var dfd = $.Deferred();
dfd.fail(callbackFunc);
dfd.reject("fail"); //'fail'

var f1 = function(){console.log("done");}, 
   f2 = function(){console.log("fail");}, 
   f3 = function(){console.log("always");};

var dfd = $.Deferred();
dfd.done(f1).fail(f2).always(f3);

//if
dfd.resolve(); //'done' 'always'
//if
dfd.reject(); //'fail' 'always'

var fun1 = function(){console.log(arguments[0]);},
  fun1 = function(){console.log(arguments[0]);};
var dfd = $.Deferred();
dfd.done(fun1);
dfd.resolve("hello"); //'hello'
dfd.done(fun2); //'hello'

var func = function(){console.log("start");} 
var dfd = $.Deferred(func); //'start' create a deferred object

var func1 = function(){console.log("1");},
   func2 = function(){console.log("2");},
   func3 = function(){console.log("3");};
var dfd = $.Deferred();
dfd.done([func1,func2],func3,[func2,func1]);
dfd.resolve(); // "1 2 3 2 1"

var func1 = function(){console.log("1");},
   func2 = function(){console.log("2");},
   func3 = function(){console.log("3");};
var dfd = $.Deferred();
dfd.fail([func1,func2],func3,[func2,func1]);
dfd.reject(); // "1 2 3 2 1"

var func = function(arg){console.log(arg);};
$.Deferred().done(func).resolve("done!"); //'done!'
var func = function(arg1,arg2){console.log(arg1.name + ',' + arg2);};
$.Deferred().done(func).resolve({name:'Lucy'},'How are you!'); // 'Lucy,How are you!'

var func = function () {
  console.log(this.name + ',' + arguments[0] + ' ' + arguments[1] + ' ' + arguments[2]);
};
$.Deferred().done(func).resolveWith({ name: "Lucy" }, ["How", "are", "you!"]);//'Lucy,How are you!'

var func = function(arg){console.log(arg);};
$.Deferred().fail(func).reject("error!"); //'error!'
var func = function(ctx,arg){console.log(ctx.name + ',' + arg);};
$.Deferred().fail(func).reject({name:'Mark'},'What happend!'); // 'Mark,What happend!'

var func = function () {
  console.log(this.name + ',' + arguments[0] + ' ' + arguments[1]);
};
$.Deferred().fail(func).rejectWith({ name: "Mark" }, ["what", "happend!"]); // 'Mark,What happend!'

function asyncEvent() {
   var dfd = jQuery.Deferred();

    // Resolve after a random interval
    setTimeout(function () {
       dfd.resolve("hurray");
    }, Math.floor(400 + Math.random() * 2000));

    // Reject after a random interval
    setTimeout(function () {
       dfd.reject("sorry");
    }, Math.floor(400 + Math.random() * 2000));

    // Show a "working..." message every half-second
    setTimeout(function working() {
       if (dfd.state() === "pending") {
          dfd.notify("working... ");
           setTimeout(working, 500);
        }
     }, 1);

      // Return the Promise so caller can't change the Deferred
      return dfd.promise();
 }

// Attach a done, fail, and progress handler for the asyncEvent
$.when(asyncEvent()).then(
    function (status) {
       alert(status + ", things are going well");
    },
    function (status) {
       alert(status + ", you fail this time");
    },
    function (status) {
       alert(status);
    }
);

var obj = {
  hello: function (name) {
    alert("Hello " + name);
  }
},
// Create a Deferred
dfd = $.Deferred();

// Set object as a promise
dfd.promise(obj);

// Resolve the deferred
dfd.resolve("John");

// Use the object as a Promise
obj.done(function (name) {
   obj.hello(name); // will alert "Hello John"
}).hello("Karl");

function func() {
  var dfd = $.Deferred();
  setTimeout(function () {
    dfd.resolve("hurry");
  }, 500);
  return dfd.promise();
};

$.when(func()).done(function (arg) {
  alert(arg); /*alert "hurry"*/
});

$.when( { name: 123 } ).done(
  function(arg) { alert(arg.name); } /* alerts "123" */
);

$.when().state(); // "resolved"

var d1 = $.Deferred();
var d2 = $.Deferred();
 
$.when( d1, d2 ).done(function ( v1, v2 ) {
  console.log( v1 ); // "Fish"
  console.log( v2 ); // "Pizza"
});
 
d1.resolve( "Fish" );
d2.resolve( "Pizza" );

var filterResolve = function () {
   var dfd = $.Deferred(),
     filtered = dfd.then(function (value) { return value * 2; });
   dfd.resolve(5);
   filtered.done(function (value) { console.log(value); });
};
filterResolve(); //'10'

var defer = $.Deferred(),
   filtered = defer.then(null, function (value) {
     return value * 3;
   });

defer.reject(6);
filtered.fail(function (value) {
   alert("Value is 3*6 = " + value);
});

function wait(ms) { 
  var deferred = $.Deferred(); 
  setTimeout(function(){deferred.resolve()}, ms);
  return deferred.promise(); 
}

wait(1500).then(function () {
    // After 1500ms this will be executed 
});

$.when($.ajax({}), $.ajax({}))
　　.done(function(){ alert("success！"); })
　　.fail(function(){ alert("error！"); });