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);
     })