naive javascript promise

Promise.js

const status = Symbol();
const value = Symbol();
const set = Symbol();
const listeners = Symbol();

class Promise {
  constructor(callback) {
    this[listeners] = [];
    this[status] = "pending";
    const resolve = value => {
      if (value instanceof Promise) value.then(resolve, reject);
      else this[set]("resolved", value);
    };
    const reject = error => {
      if (value instanceof Promise) value.then(resolve, reject);
      else this[set]("rejected", error);
    };
    callback(resolve, reject);
  }
  [set](state, data) {
    if (this[status] !== "pending") return;
    this[status] = state;
    this[value] = data;
    for (listener of this[listeners]) listener();
    delete this[listeners];
  }
  then(onResolve, onReject) {
    return new Promise((resolve, reject) => {
      const callBack = (callback, reason) => {
        try {
          if (!callback) {
            reason(this[value]);
          } else {
            const value = callback(this[value]);
            if (value instanceof Promise) value.then(resolve, reject);
            else resolve(value);
          }
        } catch (error) {
          reject(error);
        }
      };
      const check = () => {
        switch (this[status]) {
          case "resolved":
            callBack(onResolve, resolve);
            break;
          case "rejected":
            callBack(onReject, reject);
            break;
          case "pending":
            this[listeners].push(check);
            break;
        }
      };
      setTimeout(check);
    });
  }
  static resolve(value) {
    return new Promise((resolve, reject) => resolve(value));
  }
  static reject(value) {
    return new Promise((resolve, reject) => reject(value));
  }
}