class promise {

  constructor(fn) {

    this.data = null;

    this.err = null;

    this.isPromise = false;

    this.errFn = null;

    this.queue = [];

    this.run = this.run.bind(this);

    this.error = this.error.bind(this);

    this.then = this.then.bind(this);

    this.catch = this.catch.bind(this);

    this.reslove = this.reslove.bind(this);

    this.reject = this.reject.bind(this);

    this.setData = this.setData.bind(this);

    this.getData = this.getData.bind(this);

    this.setQueue = this.setQueue.bind(this);

    this.setErrFn = this.setErrFn.bind(this);

    this.getErrFn = this.getErrFn.bind(this);

    this.setPromise = this.setPromise.bind(this);

    this.getPromise = this.getPromise.bind(this);

    fn(this.reslove, this.reject);

    return this;

  }

  setPromise() {

    this.isPromise = !this.isPromise;

  }

  getPromise() {

    return this.isPromise;

  }

  setErrFn(fn) {

    this.errFn = fn;

  }

  getErrFn() {

    return this.errFn;

  }

  setQueue(fn) {

    this.queue.push(fn);

  }

  getQueue() {

    return this.queue;

  }

  setData(data) {

    this.data = data;

  }

  getData() {

    return this.data;

  }

  setErr(err) {

    this.err = err;

  }

  getErr() {

    return this.err;

  }

  reslove(data) {

    if (this.getPromise()) return;

    this.setPromise();

    this.setData(data);

    this.run();

  }

  reject(err) {

    if (this.getPromise()) return;

    this.setPromise();

    this.setErr(err);

    this.error();

  }

  then(fn) {

    this.setQueue(fn);

    return this;

  }

  catch(fn) {

    this.setErrFn(fn);

  }

  run() {

    const queue = this.getQueue();

    let ret = this.getData();

    for(let i = 0; i < queue.length; i++) {

      // 下面三种方式都可以实现想要的效果

      process.nextTick(() => {

        ret = queue[i](ret);

      });

      // setImmediate(() => {

      //   ret = queue[i](ret);

      // });

      // setTimeout(() => {

      //   ret = queue[i](ret);

      // }, 0);

    }

  }

  error() {

    // 下面三种方式都可以实现想要的效果

    process.nextTick(() => {

      this.setErrFn(fn)

    });

    // setImmediate(() => {

    //   this.setErrFn(fn)

    // });

    // setTimeout(() => {

    //   this.getErrFn()(this.getErr());

    // }, 0);

  }

}

const p = new promise((res, rej) => {

  setTimeout(() => {

    console.log('s1');

    setTimeout(() => {

      console.log('s2');

      setTimeout(() => {

        console.log('s3');

        res('res');

        rej('rej');

        console.log('s4');

      }, 1000);

    }, 1000);

  }, 1000);

});

let pp = p

.then((data) => {

  console.log(data);

  return 't2';

})

.then((data) => {

  console.log(data);

  return 't3';

});

pp.then((data) => {

  console.log(data);

}).catch((err) => {

  console.log(err);

});