javascript - Puppeteer 等待所有图像加载然后截图

Question

我正在使用Puppeteer尝试在所有图像加载后截取网站的屏幕截图，但无法使其正常工作。

这是到目前为止我得到的代码，我使用https://www.digg.com作为示例网站：

const puppeteer = require('puppeteer');

(async () => {
    const browser = await puppeteer.launch();
    const page = await browser.newPage();
    await page.goto('https://www.digg.com/');

    await page.setViewport({width: 1640, height: 800});

    await page.evaluate(() => {
        return Promise.resolve(window.scrollTo(0,document.body.scrollHeight));
    });

    await page.waitFor(1000);

    await page.evaluate(() => {
        var images = document.querySelectorAll('img');

        function preLoad() {

            var promises = [];

            function loadImage(img) {
                return new Promise(function(resolve,reject) {
                    if (img.complete) {
                        resolve(img)
                    }
                    img.onload = function() {
                        resolve(img);
                    };
                    img.onerror = function(e) {
                        resolve(img);
                    };
                })
            }

            for (var i = 0; i < images.length; i++)
            {
                promises.push(loadImage(images[i]));
            }

            return Promise.all(promises);
        }

        return preLoad();
    });

    await page.screenshot({path: 'digg.png', fullPage: true});

    browser.close();
})();

Answer 1

有一个内置选项：

await page.goto('https://www.digg.com/', {"waitUntil" : "networkidle0"});

networkidle0 - 当至少 500 毫秒内没有超过 0 个网络连接时，考虑完成导航

networkidle2 - 当至少 500 毫秒的网络连接不超过 2 个时，考虑完成导航。

PS 当然，如果您使用的是 Twitter 等无限滚动单页应用程序，则它不会起作用。

Answer 2

另一种选择，实际评估以在加载所有图像时获取回调

此选项也适用于不支持等待选项的setContentnetworkidle0

await page.evaluate(async () => {
  const selectors = Array.from(document.querySelectorAll("img"));
  await Promise.all(selectors.map(img => {
    if (img.complete) return;
    return new Promise((resolve, reject) => {
      img.addEventListener('load', resolve);
      img.addEventListener('error', reject);
    });
  }));
})

Answer 3

等待延迟加载图像

您可能需要考虑首先使用一种方法向下滚动，例如Element.scrollIntoView()考虑延迟加载图像：

await page.goto('https://www.digg.com/', {
  waitUntil: 'networkidle0', // Wait for all non-lazy loaded images to load
});

await page.evaluate(async () => {
  // Scroll down to bottom of page to activate lazy loading images
  document.body.scrollIntoView(false);

  // Wait for all remaining lazy loading images to load
  await Promise.all(Array.from(document.getElementsByTagName('img'), image => {
    if (image.complete) {
      return;
    }

    return new Promise((resolve, reject) => {
      image.addEventListener('load', resolve);
      image.addEventListener('error', reject);
    });
  }));
});

Answer 4

我面临着完全相同的问题。我觉得解决方案将涉及使用：

await page.setRequestInterceptionEnabled(true);

page.on('request', interceptedRequest => {
    //some code here that adds this request to ...
    //a list and checks whether all list items have ...
    //been successfully completed!
});

https://github.com/GoogleChrome/puppeteer/blob/master/docs/api.md#pagesetrequestinterceptionenabledvalue

Answer 5

我使用page.setViewPort(...)方法找到了适用于多个站点的解决方案，如下所示：

const puppeteer = require('puppeteer');

async(() => {
    const browser = await puppeteer.launch({
        headless: true, // Set to false while development
        defaultViewport: null,
        args: [
            '--no-sandbox',
            '--start-maximized', // Start in maximized state
        ],
    });

    const page = await = browser.newPage();
    await page.goto('https://www.digg.com/', {
        waitUntil: 'networkidle0', timeout: 0
    });

    // Get scroll width and height of the rendered page and set viewport
    const bodyWidth = await page.evaluate(() => document.body.scrollWidth);
    const bodyHeight = await page.evaluate(() => document.body.scrollHeight);
    await page.setViewport({ width: bodyWidth, height: bodyHeight });

    await page.waitFor(1000);
    await page.screenshot({path: 'digg-example.png' });
})();