javascript 如何在chrome headless+puppeteer评估（）中使用xpath？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/48448586/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to use xpath in chrome headless+puppeteer evaluate()?
提问by MevatlaveKraspek
How can I use $x()to use xpath expressioninside a page.evaluate()?
我怎样才能在 a 中$x()使用xpath 表达式page.evaluate()？
As far as pageis not in the same context, I tried $x()directly (like I would do in chrome dev tools), but no cigar.
至于page不是在同一上下文中，我$x()直接尝试（就像我在 chrome 开发工具中所做的那样），但没有雪茄。
The script goes in timeout.
脚本进入超时状态。
回答by Everettss
$x()is not a standard JavaScript method to select element by XPath. $x()it's only a helper in chrome devtools. They claim this in the documentation:
$x()不是通过 XPath 选择元素的标准 JavaScript 方法。$x()它只是chrome devtools 中的一个帮手。他们在文档中声称：
Note: This API is only available from within the console itself. You cannot access the Command Line API from scripts on the page.
注意：此 API 仅在控制台本身内可用。您无法从页面上的脚本访问命令行 API。
And page.evaluate()is treated here as a "scripts on the page".
并且page.evaluate()在此处被视为“页面上的脚本”。
You have two options:
您有两个选择：
Here is a example of selecting element (featured article) inside page.evaluate():
以下是选择内部元素（特色文章）的示例page.evaluate()：
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
await page.goto('https://en.wikipedia.org', { waitUntil: 'networkidle2' });
const text = await page.evaluate(() => {
// $x() is not a JS standard -
// this is only sugar syntax in chrome devtools
// use document.evaluate()
const featureArticle = document
.evaluate(
'//*[@id="mp-tfa"]',
document,
null,
XPathResult.FIRST_ORDERED_NODE_TYPE,
null
)
.singleNodeValue;
return featureArticle.textContent;
});
console.log(text);
await browser.close();
})();
- Select element by Puppeteer
page.$x()and pass it topage.evaluate()
- 通过 Puppeteer 选择元素
page.$x()并将其传递给page.evaluate()
This example achieves the same results as in the 1. example:
此示例实现了与 1. 示例相同的结果：
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
await page.goto('https://en.wikipedia.org', { waitUntil: 'networkidle2' });
// await page.$x() returns array of ElementHandle
// we are only interested in the first element
const featureArticle = (await page.$x('//*[@id="mp-tfa"]'))[0];
// the same as:
// const featureArticle = await page.$('#mp-tfa');
const text = await page.evaluate(el => {
// do what you want with featureArticle in page.evaluate
return el.textContent;
}, featureArticle);
console.log(text);
await browser.close();
})();
Hereis a related question how to inject $x()helper function to your scripts.
这是一个相关的问题如何将$x()辅助函数注入您的脚本。
回答by Grant Miller
If you insist on using page.$x(), you can simply pass the result to page.evaluate():
如果你坚持使用page.$x()，你可以简单地将结果传递给page.evaluate()：
const example = await page.evaluate(element => {
return element.textContent;
}, (await page.$x('//*[@id="result"]'))[0]);
