JS返回不等待等待[重复]答案

【问题标题】：JS return doesn't wait for await [duplicate]JS返回不等待等待[重复]
【发布时间】：2018-06-27 01:32:45
【问题描述】：

我正在尝试使用异步等待。

我的应用是这样开始的

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 总是作为空数组返回。这是getJobList 函数

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
}

如你所见，我将async关键字放在它前面，

我已经将async关键字放在each的回调中

并将await 放在所有异步操作的前面。

each 的回调中的console.log 打印填充了值的数组

但似乎return 在each 之前有效

即使前面有await关键字。

还有getJobDetailsHTML 以防万一。这是一个简单的功能，似乎工作得很好

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

【问题讨论】：

标签： javascript ecmascript-2017

【解决方案1】：

我认为jobsInDom.each 是同步函数，所以将 await 放在前面不会给你想要的效果。因此，您需要以某种方式获得在所有作业的处理完成时解决的承诺，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);

【讨论】：