分析ES 6 Promise

function _Promise(...args) {
  this.status = "pending";
  this.msg = "";
  const process = args[0];
  process(
    (...args) => {
      this.status = "resolve";
      this.msg = args[0];
    },
    (...args) => {
      this.status = "reject";
      this.msg = args[0];
    }
  );
  return this;
}
_Promise.prototype.then = function(...args) {
  if (this.status == "resolve") {
    args[0](this.msg);
  }
  if (this.status == "reject" && arguments[1]) {
    args[1](this.msg);
  }
};
//    
const mm = new _Promise((resolve, reject) => {
  resolve("123");
});
mm.then(
  msg => {
    console.log(msg);
    console.log("ok!");
  },
  () => {
    console.log("fail!");
  }
);

const test = new Promise((resolve, reject) => {
  resolve(123)
})

test.then((msg) => {
  console.log(msg)
  console.log('ok')
} )