try.js

/**
 * An example to try to call API multiple times
 */
'use strict';

const maxTryTimes = 3;
const tryTimeInterval = 500;

/**
 * try multiple times to access server API
 * @return {Promise}
 */
function tryMultiTimesToServer() {
  const server = new Server();
  let currentTryTime = 0;

  function tryServer(resolve, reject) {
    ++currentTryTime;
    if (currentTryTime > maxTryTimes) {
      return reject('exceed max times');
    }

    const delayTime = currentTryTime === 1 ? 0 : tryTimeInterval;
    console.log(`\ntry to fetch data from server ${currentTryTime} time...`);
    callApiWithWrapper(server, delayTime)
      .then(data => {
        if (data.success) {
          resolve(data.data);
        } else {
          if (data.err === 'rate limit') {
            tryServer(resolve, reject);
          } else {
            reject(data.err);
          }
        }
      });
  }

  return new Promise(tryServer);

}

/**
 * Call API with a wrapper to adapt promise and delay the request
 *
 * We have to have a wrapper to deal with the original API call,
 * cuz we cannot chain promise' reject
 * @param  {Number} delayTime
 * @return {Promise}
 */
function callApiWithWrapper(server, delayTime) {
  return new Promise((resolve, reject) => {
    delay(() => {
      server.fetch()
        .then(data => {
          resolve({
            success: true,
            data,
          });
        })
        .catch(resp => {
          resolve({
            success: false,
            err: resp.err,
          });
        });
    }, delayTime);
  });
}

function delay(callback, delayTime) {
  if (delayTime === 0) {
    callback();
  } else {
    setTimeout(callback, delayTime);
  }
}

// this is a mock for server API
class Server {
  constructor(hitRateLimitProbability = 0.5, downProbability = 0.15) {
    this.hitRateLimitProbability = hitRateLimitProbability;
    this.downProbability = downProbability;
  }

  random(probability) {
    return Math.random() < probability;
  }

  fetch() {
    console.log('SERVER_RESPOND: server receive request...');
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        // check if server is down
        if (this.random(this.downProbability)) {
          console.log('SERVER_RESPOND: server down...');
          return reject({
            err: 'server down',
          });
        }

        // check rate limit
        if (this.random(this.hitRateLimitProbability)) {
          console.log('SERVER_RESPOND: rate limit...');
          return reject({
            err: 'rate limit',
          });
        }

        console.log('SERVER_RESPOND: server data!!!');
        return resolve({
          data: 'server data',
        });
      });
    });
  }
}

// test code
tryMultiTimesToServer()
  .then(data => {
    console.log('\nOUTPUT:', data);
  })
  .catch(err => {
    console.log('\nOUTPUT:', err);
  });