Puppeteer: How to get the contents of each element

问题:

I'm trying to achieve something very trivial: Get a list of elements, and then do something with the innerText of each element.

const tweets = await page.$$('.tweet');

From what I can tell, this returns a nodelist, just like the document.querySelectorAll() method in the browser.

How do I just loop over it and get what I need? I tried various stuff, like:

[...tweets].forEach(tweet => {
  console.log(tweet.innerText)
});

回答1:

page.$$():

You can use a combination of elementHandle.getProperty() and jsHandle.jsonValue() to obtain the innerText from an ElementHandle obtained with page.$$():

const tweets = await page.$$('.tweet');

for (let i = 0; i < tweets.length; i++) {
  const tweet = await (await tweets[i].getProperty('innerText')).jsonValue();
  console.log(tweet);
}

If you are set on using the forEach() method, you can wrap the loop in a promise:

const tweets = await page.$$('.tweet');

await new Promise((resolve, reject) => {
  tweets.forEach(async (tweet, i) => {
    tweet = await (await tweet.getProperty('innerText')).jsonValue();
    console.log(tweet);
    if (i === tweets.length - 1) {
      resolve();
    }
  });
});

page.evaluate():

Alternatively, you can skip using page.$$() entirely, and use page.evaluate():

const tweets = await page.evaluate(() => Array.from(document.getElementsByClassName('tweet'), e => e.innerText));

tweets.forEach(tweet => {
  console.log(tweet);
});

回答2:

According to puppeteer docs here, $$ Does not return a nodelist, instead it returns a Promise of Array of ElementHandle. It's way different then a NodeList.

There are several ways to solve the problem.

1. Using built-in function for loops called page.$$eval

This method runs Array.from(document.querySelectorAll(selector)) within the page and passes it as the first argument to pageFunction.

So to get innerText is like following,

// Find all .tweet, and return innerText for each element, in a array.
const tweets = await page.$$eval('.tweet', element => element.innerText);

2. Pass the elementHandle to the page.evaluate

Whatever you get from await page.$$('.tweet') is an array of elementHandle. If you console, it will say JShandle or ElementHandle depending on the type.

Forget the hard explanation, it's easier to demonstrate.

// let's just call them tweetHandle 
const tweetHandles = await page.$$('.tweet');

// loop thru all handles
for(const tweethandle of tweetHandles){

   // pass the single handle below
   const singleTweet = await page.evaluate(el => el.innerText, tweethandle)

   // do whatever you want with the data
   console.log(singleTweet) 
}

Of course there are multiple ways to solve this problem, Grant Miller also answered few of them in the other answer.