将重击传递给伪造者的$ .eval [英] Passing a thunk to puppeteer's $.eval

问题描述

函数 setValue 接收一个值并返回一个函数.在第二个函数中，我尝试控制台记录 value 的值，但得到

The function setValue receives a value and returns a function. Inside the second function I'm trying to console log the value of value but I get

Error: Evaluation failed: ReferenceError: value is not defined

下面的代码.可以在 try-puppeteer 上进行测试，只需复制并粘贴我的代码并删除要求语句.

My code bellow. It can be tested on try-puppeteer, just copy and paste my code and remove the require statement.

const puppeteer = require('puppeteer');

(async () => {
  const USERNAME = 'helloworld';
  const setValue = (value) => (input) => { console.log(value) };

  const browser = await puppeteer.launch();
  const page = await browser.newPage();

  await page.goto('http://example.com');
  await page.$eval('.selector', setValue(USERNAME));

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

推荐答案

对于在Node.js中执行并在浏览器中评估代码(量角器，TestCafe，噩梦等)的任何库，这都是一个常见问题.函数被字符串化并作为字符串传递给浏览器.(input)=>的原始范围{console.log(value)} 丢失，并且 value 应该是未定义的全局变量.

This is a problem that is common to any library that is executed in Node.js and evaluates code in browser (Protractor, TestCafe, Nightmare, etc). A function is stringified and passed to a browser as a string. Original scope of (input) => { console.log(value) } is lost, and value is expected to be a global, which is undefined.

作为文档提及，应该将其他参数传递给 $ eval .

As the documentation mentions, additional arguments are supposed to be passed to $eval.

应该是:

await page.$eval('.selector', (el, value) => { console.log(value) }, USERNAME);

console.log 可以使用，但显然不会在Node控制台中显示任何内容，因为它是指浏览器控制台.

console.log will work but obviously, won't display anything in Node console, because it refers to browser console.

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