How crawlers download JavaScript images

In Web development, JavaScript is a very important programming language that can achieve many interesting functions. Many websites use JavaScript to achieve dynamic effects and load images on web pages. How to download these JavaScript-loaded images is an important question for someone who wants to crawl this information. This article will introduce some methods to solve this problem.

The first method is to use the Selenium library. Selenium is an automated testing tool that can automatically simulate user interactions, including clicks, input, etc. We can use this feature to get images loaded by JavaScript. The specific process is as follows:

1. Install the Selenium library and driver (such as ChromeDriver)

2. Use Selenium to open the web page and scroll down

3. Find the image element XPath or CSS selector, and use Selenium to get the element

4. Use Selenium to get the address of the element and download

The advantage of this method is that it is simple and easy to use, requiring only a small amount of The code can be easily implemented. But its disadvantage is that it is slower because it needs to simulate human operation, and it needs to start a complete browser process.

The second method is to use the Requests-HTML library. Requests-HTML is an HTML parser based on the Requests library. It can convert web pages into HTML documents and use BeautifulSoup or the lxml library to parse the HTML. In this way, we can get the address of the image loaded by JavaScript. The specific process is as follows:

1. Install the Requests-HTML library and HTML parser (such as BeautifulSoup or lxml)

2. Use Requests-HTML to download web pages and parse HTML

3. Find the CSS selector of the image element and use Requests-HTML to obtain the element

4. Get the address of the image from the element and download it

The advantage of this method is that it is faster Fast because it doesn't require starting a full browser process. But its disadvantage is that it is not suitable for web pages rendered using JavaScript, because Requests-HTML can only get the HTML that has been loaded.

The third method is to use the Pyppeteer library. Pyppeteer is a Python version of the Google Chrome development kit. It can interact with the browser and obtain information from the browser. This approach is similar to Selenium, but faster. The specific process is as follows:

1. Install the Pyppeteer library and puppeteer package

2. Use Pyppeteer to open the web page and scroll down

3. Find the XPath or CSS selection of the image element and use Pyppeteer to get the element

4. Use Pyppeteer to get the address of the element and download

The advantage of this method is that it is faster, and compared with Selenium, it does not A full browser process needs to be started. The disadvantage is that additional packages and libraries need to be installed and the amount of code is large.

In general, the above three methods can all be used to download JavaScript images. Which method to choose depends on your needs and personal preferences. No matter which method, we need to understand the execution process of JavaScript and find a suitable solution.

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