Node.js中如何使用async函数

const rp = require('request-promise')
async function main () {
 const result = await rp('https://google.com')
 const twenty = await 20
 
 // 睡个1秒钟
 await new Promise (resolve => {
  setTimeout(resolve, 1000)
 })
 return result
}
main()
 .then(console.log)
 .catch(console.error)

const util = require('util')
const {readFile} = require('fs')
const readFileAsync = util.promisify(readFile)
async function main () {
 const result = await readFileAsync('.gitignore')
 return result
}
main()
 .then(console.log)
 .catch(console.error)

const express = require('express')
const app = express()
app.get('/', async (request, response) => {
 // 在这里等待 Promise
 // 如果你只是在等待一个单独的 Promise，你其实可以直接将将它作为返回值返回，不需要使用 await 去等待。
 const result = await getContent()
 response.send(result)
})
app.listen(process.env.PORT)

const awaitHandlerFactory = (middleware) => {
 return async (req, res, next) => {
  try {
   await middleware(req, res, next)
  } catch (err) {
   next(err)
  }
 }
}
// 然后这样使用：
app.get('/', awaitHandlerFactory(async (request, response) => {
 const result = await getContent()
 response.send(result)
}))

async function main () {
 const user = await Users.fetch(userId)
 const product = await Products.fetch(productId)
 await makePurchase(user, product)
}

async function main () {
 const [user, product] = await Promise.all([
  Users.fetch(userId),
  Products.fetch(productId)
 ])
 await makePurchase(user, product)
}

async function main () {
 await new Promise((resolve, reject) => {
  reject(new Error('error'))
 })
}
main()
 .then(console.log)

const util = require('util')
async function main () {
 try {
  await new Promise((resolve, reject) => {
   reject(new Error('