promise.js

const resolved = Promise.resolve();


class Deferred {
  constructor() {
    const p = new Promise((resolve, reject) => {
      this.resolve = resolve;
      this.reject = reject;
    });
    this.then = p.then.bind(p);
    this.catch = p.catch.bind(p);
  }
}


function delay(time = 0) {
  if (!time) {
    return resolved;
  }
  return new Promise(r => setTimeout(r, time));
}

function sequence(array, func) {
  return (array || []).reduce((seq, ...args) => seq.then(() => func(...args)), resolved);
}


function promiseProxy(func, isOnce, isResolve) {
  let result;
  let promise;
  let run = false;
  function reset() {
    run = false;
  }
  return (...args) => {
    if (isOnce && result) {
      return isResolve ? Promise.resolve(result) : Promise.reject();
    }
    if (run && promise) {
      return promise;
    }
    run = true;
    promise = new Promise((res, rej) => {
      const p = func.apply(null, args);
      if (p && p.then && typeof p.then === 'function') {
        p.then(r => {
          reset();
          result = r;
          res(r);
        }).catch(e => {
          reset();
          rej(e);
        });
      } else {
        reset();
        res(p);
      }
    });
    return promise;
  };
}
function onceResolve(func) {
  return promiseProxy(func, true, true);
}
function onceReject(func) {
  return promiseProxy(func, true);
}
function waitFinish(func) {
  return promiseProxy(func);
}