JavaScript工具函数

asyncSequentializer.js

const asyncSequentializer = (() => {
  const toPromise = (x) => {
    if(x instanceof Promise) { // if promise just return it
      return x;
    }
    
    if(typeof x === 'function') {
      // if function is not async this will turn its result into a promise
      // if it is async this will await for the result
      return (async () => await x())();
    }
    
    return Promise.resolve(x)
  }
  
  return (list) => {
    const results = [];
    
    return list
      .reduce((lastPromise, currentPromise) => {
        return lastPromise.then(res => {
          results.push(res); // collect the results
          return toPromise(currentPromise);
        });
      }, toPromise(list.shift()))
      // collect the final result and return the array of results as resolved promise
      .then(res => Promise.resolve([...results, res]));
  }
})();

poll.js

// 轮询数据
// 如果你需要持续检查数据更新，但系统中没有 WebSocket，则可以使用这个工具来执行操作。它非常适合上传文件时，想要持续检查文件是否已完成处理的情况，或者使用第三方 API（例如 dropbox 或 uber）并且想要持续检查过程是否完成或骑手是否到达目的地的情况。
async function poll(fn, validate, interval = 2500) {
  const resolver = async (resolve, reject) => {
    try { // catch any error thrown by the "fn" function
      const result = await fn(); // fn does not need to be asynchronous or return promise
      // call validator to see if the data is at the state to stop the polling
      const valid = validate(result);
      if (valid === true) {
        resolve(result);
      } else if (valid === false) {
        setTimeout(resolver, interval, resolve, reject);
      } // if validator returns anything other than "true" or "false" it stops polling
    } catch (e) {
      reject(e);
    }
  };
  return new Promise(resolver);
}

stringify.js

const stringify = (() => {
  const replacer = (key, val) => {
    if(typeof val === 'symbol') {
      return val.toString();
    }
    if(val instanceof Set) {
      return Array.from(val);
    }
    if(val instanceof Map) {
      return Array.from(val.entries());
    }
    if(typeof val === 'function') {
      return val.toString();
    }
    return val;
  }
  
  return (obj, spaces = 0) => JSON.stringify(obj, replacer, spaces)
})();