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等待async变得更漂亮,但没有承诺那么多功能

es6-promise async-await

standup75 · 技术社区 · 7 年前

下面是我使用wait/async编写的漂亮代码

monthlyBuckets(req, res) {
  const monthlyBuckets = []
  const now = DateTime.local()
  let date = config.beginningOfTime
  while (date < now) {
    monthlyBuckets.push({
      epoch: date.toMillis(),
      month: date.month,
      year: date.year,
      actions: await redis.get(`actions_monthly_${date.year}_${date.month}`),
      interested: await redis.scard(`sinterested_monthly_${date.year}_${date.month}`),
      adventurous: await redis.scard(`sadventurous_monthly_${date.year}_${date.month}`),
      active: await redis.scard(`sactive_monthly_${date.year}_${date.month}`),
    })
    date = date.plus({month: 1})
  }
  res.status(200).json(monthlyBuckets)
}

我很喜欢,但是不同时发出这么多请求会导致请求时间接近3秒。

下面是我没有async/await的丑陋解决方案,只是承诺:

monthlyBuckets(req, res) {
    const monthlyBuckets = []
    const actions = []
    const interested = []
    const adventurous = []
    const active = []
    const now = DateTime.local()
    let date = config.beginningOfTime
    let entryCount = 0
    while (date < now) {
      monthlyBuckets.push({
        epoch: date.toMillis(),
        month: date.month,
        year: date.year,
      })
      actions.push(redis.get(`actions_monthly_${date.year}_${date.month}`))
      interested.push(redis.scard(`sinterested_monthly_${date.year}_${date.month}`))
      adventurous.push(redis.scard(`sadventurous_monthly_${date.year}_${date.month}`))
      active.push(redis.scard(`sactive_monthly_${date.year}_${date.month}`))
      date = date.plus({month: 1})
      entryCount++
    }
    const data = await Promise.all(actions.concat(interested).concat(adventurous).concat(active))
    for (let i = 0; i < entryCount; i++) {
      monthlyBuckets[i].actions = data[i]
      monthlyBuckets[i].interested = data[entryCount + i]
      monthlyBuckets[i].adventurous = data[entryCount * 2 + i]
      monthlyBuckets[i].active = data[entryCount * 3 + i]
    }
    res.status(200).json(monthlyBuckets)
  }
}

这并不漂亮,但它能在200毫秒内完成任务

能给我漂亮又高效的吗?

1 回复 | 直到 7 年前

Jannes Botis 7 年前

上述代码的问题在于,您试图:

使用 一个承诺。全部() 为了所有的承诺
处理中所有响应的输出 一次回拨

虽然这不是一个错误,但它可能会导致难以“阅读”的代码。

代码可以写成:

while (date < now) {
  let dateData = {
    epoch: date.toMillis(),
    month: date.month,
    year: date.year,
  };
  let promiseData = Promise.all([
      dateData, // dataData is cast(made to) automatically into a promise
      redis.get(`actions_monthly_${date.year}_${date.month}`),
      redis.scard(`sinterested_monthly_${date.year}_${date.month}`),
      redis.scard(`sadventurous_monthly_${date.year}_${date.month}`),
      redis.scard(`sactive_monthly_${date.year}_${date.month}`)
  ]).then([data, actions, interested, adventurous, active] => {
      // process the data here for each month
      data.actions = actions;
      data.interested = interested;
      data.adventurous = adventurous;
      data.active = active;
      return data;
});
  monthlyBuckets.push(promiseData);
  date = date.plus({month: 1});
}

const data = await Promise.all(monthlyBuckets);
res.status(200).json(data);

改变的是

将承诺分组 每个月
处理一个月的 一组承诺,而不是所有的承诺 并根据需要返回数据。

Promise.all([
       Promise.all([ ...]),
       Promise.all([ ...]),
       singlePromise,
       ...
]);

处理承诺,例如:

promiseProcessed1 = promise1.then(callback1);
promiseProcessed12 = Promise.all([promise1, promise2]).then(callback2);

或者重复使用承诺,例如:

promiseProcessed1 = promise1.then(callback1);
promiseProcessed12 = Promise.all([promise1, promise2]).then(callback2);
resultDatapromise = Promise.all([promise1, promise2, promiseProcessed1, promiseProcessed12]).then(callback2);

工具书类

s.d 7 年前

在这种情况下,采取不同的步骤可能会有所帮助。例子:

function createBucket(date, ops){
    const b = {
        epoch: date.toMillis(),
        month: date.month,
        year: date.year,
        actions: redis.get(`actions_monthly_${date.year}_${date.month}`),
        interested: redis.scard(`sinterested_monthly_${date.year}_${date.month}`),
        adventurous: redis.scard(`sadventurous_monthly_${date.year}_${date.month}`),
        active: redis.scard(`sactive_monthly_${date.year}_${date.month}`),
    }

    const promised = ['actions','interested', 'adventurous', 'active'];
    promised.forEach(p => ops.push(async () => {b[p] = await b[p]}));
}

async function monthlyBuckets(req,res){
    const monthlyBuckets = []
    const now = DateTime.local()
    let date = config.beginningOfTime

    const ops = [];
    while (date < now) {
      monthlyBuckets.push(createBucket(date,ops));
      date = date.plus({month: 1})
    }

    await Promise.all(ops);
    res.status(200).json(monthlyBuckets)
}