我如何从 puppeteer 中的 page.evaluate() 返回一个值? [英] How do i return a value from page.evaluate() in puppeteer?

问题描述

我正在尝试从使用 Puppeteer 构建的 YouTube 抓取工具中的 page.evaluate() 正文中获取值.我无法从 page.evaluate() 返回结果.我如何实现这一目标?代码如下:

I am trying to get a value from inside page.evaluate() body in my YouTube scraper that I've built using Puppeteer. I am unable to return the result from page.evaluate(). How do I achieve this? Here's the code:

let boxes2 = []
        const getData = async() => {
            return await page.evaluate(async () => { // scroll till there's no more room to scroll or you get at least 250 boxes  
                console.log(await new Promise(resolve => {

                    var scrolledHeight = 0  
                    var distance = 100 
                    var timer = setInterval(() => {
                        boxes = document.querySelectorAll("div.style-scope.ytd-item-section-renderer#contents > ytd-video-renderer > div.style-scope.ytd-video-renderer#dismissable")
                        console.log(`${boxes.length} boxes`)
                        var scrollHeight = document.documentElement.scrollHeight
                        window.scrollBy(0, distance)
                        scrolledHeight += distance
                        if(scrolledHeight >= scrollHeight || boxes.length >= 50){
                            clearInterval(timer)
                            resolve(Array.from(boxes))
                        }
                    }, 500)
                }))
            })
        }
        boxes2 = await getData()
        console.log(boxes2)

包装承诺的 console.log 在浏览器的控制台中打印结果数组.我只是无法在 boxes2 中调用 getData() 函数的地方获取该数组.我觉得我错过了一点点，但无法弄清楚它是什么.感谢这里的任何提示.

The console.log wrapping the promise prints the resulting array in the browser's console. I just cannot get that array in boxes2 down where I'm calling the getData() function. I feel like I'm missing out on a tiny little bit, but can't figure out what it is. Appreciate any tip here.

推荐答案

小问题是你实际上并没有从 page.evaluate 内部返回数据:

The little issue is that you don't actually return the data from inside of page.evaluate:

const getData = () => {
    return page.evaluate(async () => { 
        return await new Promise(resolve => { // <-- return the data to node.js from browser
            // scraping
        }))
    })
}

这里是 puppeteer 的一个完整的最小工作示例，它将打印数组 [ 1, 2, 3 ]:

And here's a full minimal working example for puppeteer that will print array [ 1, 2, 3 ]:

const puppeteer = require('puppeteer');

puppeteer.launch().then(async browser => {
  const page = await browser.newPage();

  boxes2 = [];

  const getData = async() => {
    return await page.evaluate(async () => {
        return await new Promise(resolve => {
          setTimeout(() => {
                resolve([1,2,3]);
          }, 3000)
      })
    })
  }  

  boxes2 = await getData();
  console.log(boxes2)

  await browser.close();
});

这篇关于我如何从 puppeteer 中的 page.evaluate() 返回一个值?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！