Promise A 规范的一个简单的浏览器端实现

简单的实现了一个promise 的规范，留着接下来模块使用。感觉还有很多能优化的地方，有时间看看源码，或者其他大神的代码

主要是Then 函数。回调有点绕人。

 !(function(win) {

   function Task(resolver) {
     if (!resolver || (typeof resolver).toUpperCase() != 'FUNCTION') {
       throw 'task arg is function,and is must';
       return;
     }

     if (!(this instanceof Task)) return new Task(resolver);

     var self = this;
     //PENDING,FULFILLED,REJECTED
     self.statu = 'PENDING';
     self.callbackok = null;
     self.callbackreject = null;

     self.value = null;
     self.reason = null;

     function resolve(data) {
       self.statu = 'FULFILLED';
       self.value = data || {};
       self.callbackok && self.callbackok(self.value);
     }

     function reject(reason) {
       self.statu = 'REJECTED';
       self.reason = reason || {};
       self.callbackreject && self.callbackreject(self.reason);
     }

     resolver(resolve, reject);

   }

   Task.all = function(arr) {

     if (!(arr instanceof Array)) {
       throw 'arr must be Task Array';
       return;
     }

     return Task(function(resolve, reject) {
       var dataarr = {};
       var len = arr.length;
       for (var i = 0; i < len; i++) {
         (function(c) {
           console.log(arr[c]);
           arr[c].then(function(data) {
             dataarr[c] = data;
             len--;
             if (len == 0) {
               var data = new Array(len);
               for (var item in dataarr) {
                 data[item] = dataarr[item];
               }
               resolve(data);
             }

           }, function(error) {
             reject(error);
           })
         })(i)
       }
     })
   }

   //创建一个成功状态的Task对象
   Task.resolve = function(value) {

     return new Task(function(resolve) {
       resolve(value);
     })
   }

   Task.prototype.then = function(onFulfilled, onRejected) {

     var task = this;

     return Task(function(resolve, reject) {

       function callback(value) {

         var ret = (typeof onFulfilled).toUpperCase() == 'FUNCTION' && onFulfilled(value) || value;

         if (isThenable(ret)) {
           ret.then(function(value) {
             resolve(value);
           }, function(reason) {
             reject(reason);
           });
         } else {
           resolve(ret);
         }
       }

       function errorback(reason) {
         reason = (typeof onRejected).toUpperCase() == 'FUNCTION' && onRejected(reason) || reason;
         reject(reason);
       }

       if (task.statu === 'PENDING') {
         task.callbackok = callback;
         task.callbackreject = errorback;
       } else if (task.statu === 'FULFILLED') {
         callback(task.value);
       } else if (task.statu === 'REJECTED') {
         errorback(task.reason);
       }

     });

   }

   var isThenable = function(obj) {
     return obj && typeof obj['then'] == 'function';
   }

   window.Task = Task;

 })(window)

下面是几种调用

串行

 var task = new Task(function(resolve, reject) {
     setTimeout(function() {
       resolve('aaaa');
     }, 100);
   })
   var task1 = function() {
     return new Task(function(resolve, reject) {
       setTimeout(function() {
         resolve('bbbb');
       }, 100);
     })
   }
   var task2 = function() {
     return new Task(function(resolve, reject) {
       setTimeout(function() {
         resolve('cccc');
       }, 100);
     })
   }
   var task3 = function() {
     return new Task(function(resolve, reject) {
       setTimeout(function() {
         reject('dddd');
       }, 100);
     })
   }
   task.then(task1).then(task2).then(task3).then(function(data) {
     console.log(data)
   }, function(error) {
       console.log(data)
   });

并行

  var task = new Task(function(resolve, reject) {
     setTimeout(function() {
       resolve('aaaa');
     }, 100);
   })
   var task2 = new Task(function(resolve, reject) {
     setTimeout(function() {
       resolve('aaaa');
     }, 100);
   })
   var task3 = new Task(function(resolve, reject) {
     setTimeout(function() {
       resolve('aaaa');
     }, 100);
   })
   var task4 = new Task(function(resolve, reject) {
     setTimeout(function() {
       resolve('aaaa');
     }, 100);
   })
   var task5 = new Task(function(resolve, reject) {
     setTimeout(function() {
       resolve('aaaa');
     }, 100);
   })
  //并行
  Task.all([task,task2,task3,task4,task5]).then(function(data){ console.log(data)})

创建一个一开始就是 释放状态的 task

Task.resolve('data').then(function(data){
         console.log(data);
     })