Implement Easy Version Promise

function Promise(fn) {

  var state = 'pending';

  var value;

  var deferred = null;

  function resolve(newValue){

  if(newValue != null &&  typeof newValue.then === 'function'){

    newValue.then(resolve, reject);

      return;

    }

    state = 'resolved';

    value = newValue;

    if(deferred){

    handle(deferred);

    }

  }

  function reject(reason){

    state = 'rejected';

    value = reason;

    if(deferred){

    handle(deferred);

    }

  }

  function handle(handler){

    if(state === 'pending'){

    deferred = handler;

        return;

    }

    var handlerCallback;

    if(state === 'resolved'){

    handlerCallback = handler.onResolved;

    }else{

    handlerCallback = handler.onRejected;

    }

    if(!handlerCallback){

    if(state === 'resolved'){

      handler.resolve(value);

      }else{

      handler.reject(value);

      }      

      return;

    }

    var ret = handlerCallback(value);

    handler.resolve(ret);

  }

  this.then = function(onResolved, onRejected){

  return new Promise(function(resolve, reject){

    handle({

      onResolved: onResolved,

        onRejected: onRejected,

        resolve: resolve,

        reject: reject

      })

    });

  }

  fn(resolve, reject);

}