javascript - 为什么函数getPrice()仅调用一次？

Question

为什么函数getPrice()在我的代码中仅被调用过一次？我认为每次 telegrambot 收到消息时，都必须调用它。还是我错了？

const Nightmare = require('nightmare')
const nightmare = Nightmare({show: true})

const TelegramBot = require('node-telegram-bot-api')
const TOKEN = ''

const bot = new TelegramBot(TOKEN, {polling: true})
console.log('Bot has been started...')

let price 

 function getPrice(){
    nightmare
        .goto('https://uk.investing.com/commodities/real-time-futures')
        .evaluate(()=>{
            let gold = document.querySelector('.pid-68-last').innerText
            let goldAug20 = document.querySelector('.pid-8830-last').innerText
            let diff = Math.abs( gold.replace(',','') - goldAug20.replace(',',''))
            return diff.toFixed(2)
        })
        .end()
        .then(data =>{
            price = data
            //console.log(price)
            return nightmare
        })
    
  }

  bot.on('message', (msg) => {
    getPrice()
    bot.sendMessage(msg.chat.id, price)
  })

Answer 1

正确的做法是，每次getPrice()事件触发时都应调用message，因此该事件可能仅触发一次。也许添加控制台日志以验证事件是否在每条消息上触发。
但是，您的代码还有另一个问题，那就是price变量将在事件发生后设置，因为它是异步的。我对Nightmare库不熟悉，但是根据您的代码，您似乎可以对async/await进行一些简单的更改以使其正常工作:

 // Add the 'async' keyword to make this an asynchronous function function
 async function getPrice(){
    // return the "promise" resulting from your chained method calls
    return nightmare
        .goto('https://uk.investing.com/commodities/real-time-futures')
        .evaluate(()=>{
            let gold = document.querySelector('.pid-68-last').innerText
            let goldAug20 = document.querySelector('.pid-8830-last').innerText
            let diff = Math.abs( gold.replace(',','') - goldAug20.replace(',',''))
            return diff.toFixed(2)
        })
        .end()
        .then(data =>{
            price = data
            //console.log(price)
            return nightmare
        })
    
  }

  // Make the callback asynchronous with the 'async' keyword
  bot.on('message', async (msg) => {
    // Use the 'await' keyword to pause execution until the promise
    // is resolved (and therefore "price" is set)
    await getPrice()
    bot.sendMessage(msg.chat.id, price)
  })

我不确定您的其余代码是否会按预期运行，但这就是您如何使异步工作按预期方式工作的方式!一定要花一些时间阅读 promises。他们需要练习来习惯，但是在Javascript中是必不可少的!