promise implementation

promisible.js

function Promisible(executor) {
  var _this = this;
  _this.status = 'pending';
  _this.result = null;
  _this.reason = null;
  _this.resolvedCallbacks = [];
  _this.rejectedCallbacks = [];

  function resolve(result) {
    if (_this.status === 'pending') {
      _this.result = result;
      _this.status = 'fulfilled';
      _this.resolvedCallbacks.forEach(fn => fn());
    }
  }
  function reject(reason) {
    if (_this.status === 'pending') {
      _this.reason = reason;
      _this.status = 'rejected';
      _this.rejectedCallbacks.forEach(fn => fn());
    }
  }

  executor(resolve, reject);
}

Promisible.prototype.then = function(onfulfilled, onrejected) {
  var _this = this;

  if (_this.status === 'resolved'){
    onfulfilled(_this.value);
  }
  if (_this.status === 'rejected'){
    onrejected(_this.reason);
  }

  if (_this.status === 'pending') {
    _this.resolvedCallbacks.push(function() {
      onfulfilled(_this.result);
    });
    _this.rejectedCallbacks.push(function() {
      onrejected(_this.reason);
    });
  }
}