node.js - puppeteer 中的 page.$eval 函数始终返回未定义

Question

我正在使用 puppeteer 和函数 page.$(selector) 来获取值。该函数返回错误“预期获取 |string| 或 |function| 作为第一个参数，但结果却是“未定义”。”我已经在 Chrome 的控制台中测试了精确的选择器，它可以工作。

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://stackoverflow.com/', {waitUntil: 'networkidle0'});
  try {
    const x = await page.$eval("body > header > div > ol.list-reset.grid.gs4 > li > a")
    console.log(firstArticle.text())
  } catch(err){
    console.log(err)
  }

  console.log(x.text())

  await browser.close();
})();

这里有什么问题吗？

Answer 1

函数 page.$eval() 必须接收两个参数，但您只发送一个。查看方法签名:

page.$eval(selector, pageFunction[, ...args])

• selector (string) A selector to query page for
• pageFunction (function(Element)) Function to be evaluated in browser context
• ...args (...Serializable|JSHandle) Arguments to pass to pageFunction
• returns: (Promise(Serializable)) Promise which resolves to the return value of pageFunction

尝试将代码更改为:

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://stackoverflow.com/', {waitUntil: 'networkidle0'});
  try {
    const elemText = await page.$eval("body > header > div > ol.list-reset.grid.gs4 > li > a", elem => elem.innerText)
    console.log('element innerText:', elemText)
  } catch(err){
    console.log(err)
  }
  await browser.close();
})();