Deferred 设计

Deferred设计

和ES6的Promise很像，设计灵感来自Deferred对象。

代码实现如下：

var wait = function() {
           var deferred = $.Deferred();
           console.log(deferred);
           var test = function() {
               console.log('开车了！');
               deferred.resolve('Max');
           }
           setTimeout(test, 2000);
           return deferred;
       }
       $.when(wait())
        .done(function() {
            console.log('done');
        })
        .fail(function() {
            console.log('fail');
        });

jQuery.extend({
        // 异步回调解决方案
        Deferred: function(func) {
            var tuples = [
                ["resolve", "done", jQuery.callbacks("once memory"), "resolved"],
                ["reject", "fail", jQuery.callbacks("once memory"), "rejected"],
                ["notify", "progress", jQuery.callbacks("memory")],
            ];
            var deferred = {};
            var state = 'pending';
            var promise = {
                state: function() {
                    return state;
                },
                then: function() {   // done, fail, progress
                },
                promise: function(obj) {
                    return obj != null ? jQuery.extend(obj, promise) : promise;
                }
            };
            tuples.forEach(function(tuple, i){
               var list = tuple[2];
               var stateString = tuple[3];
               // promise[done, fail, progress] = list.add
               promise[tuple[1]] = list.add;
               if(stateString) {
                  list.add(function() {
                    state = stateString;
                  });
               }
               deferred[tuple[0]+'With'] = list.fire;
               // deferred [resolve, reject, notify]
               deferred[tuple[0]] = function() {
                  deferred[tuple[0] + 'With'](this === deferred ? promise : this, arguments);
                  return this;
               };
            });
            // make deferred as a promise
            promise.promise(deferred);
            return deferred;
        },
        when: function(obj) {
            return obj.promise();
        }
   });