How does the Node.js client implement page display without downloading resources?

With the continuous development of Web technology, more and more websites are beginning to use JavaScript and Ajax technology to achieve more interactive page effects. As a back-end programming language based on JavaScript, Node.js’ client is increasingly used to develop web applications. However, the front-end pages of some websites need to download some resources before they can be displayed normally. Here is a common method to display pages on the Node.js client without downloading resources.

Generally, if you need to access a website on the Node.js client, you usually request the HTML page of the website, then parse the resource links in it, and then download and display the page by requesting these resources.

If you must log in to download a resource, you need to simulate login on the Node.js client and record cookies so that subsequent requests can maintain the login status. The code example is as follows:

const superagent = require('superagent');
const cheerio = require('cheerio');

superagent.post('https://example.com/login')
  .send({
    username: 'your username',
    password: 'your password'
  })
  .end((err, res) => {
    const cookie = res.headers['set-cookie'];
    superagent.get('https://example.com/secret-page')
      .set('cookie', cookie)
      .end((err, res) => {
        const $ = cheerio.load(res.text);
        console.log($('p').text());
      });
  });

In the above code, we use the superagent module to implement the operations of logging in and requesting the page. Among them, the .set() method is used to set Cookie so that we can remain logged in in subsequent requests.

However, if the download of certain resources is unnecessary, we can use some techniques to avoid downloading these unnecessary resources. For example, if we do not need to display resources such as images and videos contained on some web pages, we can change their URLs to empty strings or placeholders to avoid downloading. The sample code is as follows:

const superagent = require('superagent');
const cheerio = require('cheerio');

superagent.get('https://example.com')
  .end((err, res) => {
    const $ = cheerio.load(res.text);
    $('img').attr('src', '');  // 将所有图片链接修改为空字符串
    $('video').attr('src', 'placeholder.mp4'); // 将所有视频链接修改为占位符
    console.log($.html());
  });

In the above code, we use the cheerio module to parse the HTML page, and then use the $().attr() method to modify the resource link that needs to be modified to our the desired string.

In addition to the above methods, there is a more advanced way to achieve the effect of not downloading resources, which is to use a headless browser. Puppeteer is a headless browser library developed by Google that can be used in Node.js. Through Puppeteer, we can simulate browser behavior to access web pages, and use some advanced technologies to control page rendering and resource loading. The sample code is as follows:

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://example.com', {
    waitUntil: 'networkidle0'  // 告诉 Puppeteer 在所有网络请求结束后再进行页面渲染
  });
  await page.evaluate(() => {
    Array.from(document.querySelectorAll('img')).forEach(img => {
      img.src = '';
    });
    Array.from(document.querySelectorAll('video')).forEach(video => {
      video.src = 'placeholder.mp4';
    });
  });
  const html = await page.content();
  console.log(html);
  await browser.close();
})();

Through Puppeteer, we can modify the resource link that needs to be loaded before rendering the HTML page to achieve the effect of not downloading the resource. The advantage of this approach is that it can control the behavior of resource loading and page rendering more efficiently and accurately.

To sum up, displaying pages without downloading resources in the Node.js client can be achieved in a variety of ways. The specific method chosen depends on the actual situation. But in general, mastering these skills can give us better control over page rendering and resource loading, thereby improving application performance and user experience.

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