js中Promise的状态探究

function Promise(fn) {

  var state = 'pending';

  var value;

  var deferred;

  function resolve(newValue) {

    value = newValue;

    state = 'resolved';

    if(deferred) {

      handle(deferred);

    }

  }

  function handle(onResolved) {

    if(state === 'pending') {

      deferred = onResolved;

      return;

    }

    onResolved(value);

  }

  this.then = function(onResolved) {

    handle(onResolved);

  };

  fn(resolve);

}