a tiny promise polyfill

tinypromise

function isThenable(obj){
  if(obj && typeof obj.then === 'function'){
    return true;
  }
  return false;
}
function ChainedPromise(promise, rv, rj){
  this.success = [rv];
  this.fail = [rj];
  this.promise = promise;
  this.value = null;
}
ChainedPromise.prototype = {
  then: function(rv, rj){
    var data = this.promise.data;
    if(data.state === 2){
      if(data.flag){
        rv(this.value); 
      }else{
        rj(this.value); 
      }
    }else{
      if(rv){
        this.success.push(rv);
      }
      if(rj){
        this.fail.push(rj);  
      }
    }
    return this;
  },
  _do: function(val, isResolved){
    var _this = this;
    var jobs = isResolved ? this.success: this.fail;
    this.value = val;
    if(jobs.length){
      val = (jobs.shift())(this.value);  
      if(isThenable(val)){
        val.then(function(res){
          _this.resolve(res);
        });
        return;
      }
      this.value = val;
    }
    setTimeout(function(){
      while(jobs.length){
        val = (jobs.shift())(_this.value);  
        if(isThenable(val)){
          val.then(function(res){
            _this.resolve(res);
          });
          break;
        }
        _this.value = val;
      }
    },0);
  },
  resolve: function(val){
    this._do(val, true);
  },
  reject: function(val){
    this._do(val, false);
  }
};


function TinyPromise(fn){
  var _this = this;
  this.data = {
    success:[],
    fail:[],
    state:0, // 0:未执行、1：执行中、2：执行完成
    flag: null, // true：成功执行；false：失败执行
    value:null,
    chained:[] //链式对象
  }
  // this.chained = new ChainedPromise(this);
  setTimeout(function(){
    fn.call(_this,function(res){
      _this._exec(res, true);
    }, function(res){
      _this._exec(res, false);
    });
  },0);
}

TinyPromise.prototype = {
  then: function(rv, rj){
    var data = this.data;
    if(data.state === 2){
      if(data.flag){
        rv(data.value); 
      }else{
        rj(data.value); 
      }
    }
    if(data.state === 0){
      data.state = 1;
    }
    var chain = new ChainedPromise(this,rv, rj);
    data.chained.push(chain);
    return chain;
  },
  _exec: function (res, isResolved) {
    var data = this.data;
    var method = isResolved ? 'resolve': 'reject';
    if(data.state !== 2){
      data.value = res;
      data.state = 2;
      data.flag = !!isResolved;
      while(data.chained.length){
        (data.chained.shift())[method](res); 
      }
    }
  }
}

TinyPromise.resolve = function(value) {
  if (value && isThenable(value)) {
    return value;
  }

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

TinyPromise.reject = function(value) {
  return new TinyPromise(function(resolve, reject) {
    reject(value);
  });
};