javascript - JS返回不等待await

Question

这个问题已经有答案了:

Using async/await with a forEach loop (33 个回答)

已关闭 5 年前。

我正在尝试使用异步等待。

我的应用程序是这样启动的

axios.get(`${ROOT_URL}/ccidxann.php`)
  .catch(err => console.error('axios error get', err))
  .then(async res => {
    const html = res.data
    const jobList = await getJobList(html)
    console.log(' after each jobList', jobList)
    // jsonfile.writeFileSync('jobs.json', jobList, { flag: 'a' })
  })
  .catch(err => console.error(err))

问题是 jobList始终作为空数组返回。这是getJobList功能

async function getJobList (html) {
  const jobList = []

  const dom = new JSDOM(html)
  const { window } = dom
  const $ = require('jquery')(window)
  const jobsInDom = $('table').first().find('td > a')

  // AWAIT HERE
  await jobsInDom.each(async function (index, jobElem) {
    const name = $(jobElem).text()
    const url = $(jobElem).attr('href')
    // Another AWAIT HERE
    const jobDetailsHTML = await getJobDetailsHTML(`${ROOT_URL}/${url}`)
      .catch(err => console.error('getJobDetailsHTML err', err))
    const domDetails = new JSDOM(jobDetailsHTML)
    const { window: windowDetails } = domDetails
    const $details = require('jquery')(windowDetails)
    const jobDetailsHTMLBody = $details('body').prop('outerHTML')
    jobList.push({
      _id: url,
      name,
      detailsHTML: jobDetailsHTMLBody
    })
    console.log('in each jobList', jobList)
  }) //each
  return jobList
}

正如你所看到的，我输入了 async前面的关键字，

我已经输入了 async each回调中的关键字

并输入await在所有异步操作之前。

console.log在each的回调中打印填充有值的数组

但似乎return在 each 之前工作

即使有await前面有关键字。

这里还有getJobDetailsHTML万一。这是一个简单的功能，而且似乎工作得很好

async function getJobDetailsHTML (url) {
    // ANOTHER AWAIT HERE
    return await axios.get(url).data
}

Answer 1

我认为jobsInDom.each是同步函数，因此在前面放置await不会给您带来预期的效果。因此，您需要以某种方式获得在所有作业处理完成后解决的 promise ，如下所示:

  // handles one element and returns promise
  const jobHandler = async jobElem => {
    const name = $(jobElem).text()
    const url = $(jobElem).attr('href')
    const jobDetailsHTML = await getJobDetailsHTML(`${ROOT_URL}/${url}`)
      .catch(err => console.error('getJobDetailsHTML err', err))
    const domDetails = new JSDOM(jobDetailsHTML)
    const { window: windowDetails } = domDetails
    const $details = require('jquery')(windowDetails)
    const jobDetailsHTMLBody = $details('body').prop('outerHTML')
    jobList.push({
      _id: url,
      name,
      detailsHTML: jobDetailsHTMLBody
    })
    console.log('in each jobList', jobList)
  }

  const promises = [];

  // start processing of each element
  jobsInDom.each((index, jobElem) => promises.push(jobHandler(jobElem));

  // wait for processing of all job elements
  await Promise.all(promises);