SoFunction
Updated on 2025-03-02

Detailed explanation of how JavaScript front-end implements screenshot function

Commonly used front-end screenshot saving method

Leverage Blob objects and: You can convert the screenshot data into a blob object and then useMethod generates a temporary URL, assigning this URL to<a>TagshrefProperties, set againdownloadThe attribute is the required file name, so that the user will automatically download the image file when clicking on the link.

ToDataURL method using canvas: You can draw the screenshot onto a canvas element and then use the canvastoDataURLMethod converts the content in canvas to a data URL and creates a temporary<a>Tag, assign data URL tohrefProperties, settingsdownloadThe attribute is the required file name, thereby realizing the download function.

Leverage Blob objects and

**Generate Blob Object: **First, convert the screenshot data into a Blob object. A Blob object is an object used to represent binary data and can be created by passing the data to a Blob constructor. In this scenario, the screenshot data is usually a base64-encoded string that needs to be decoded into binary data and then converted to a blob object.

**Create temporary URL: **UseThe method generates a temporary URL. This URL points to the contents of the Blob object. The generated URL is unique and will be automatically released when the page is closed, so it is called a temporary URL.

**Create a download link: ** Assign the generated temporary URL to<a>Tagshrefproperty. At the same time, set updownloadThe attribute is the required file name, so that the user will automatically download the image file when clicking on the link.

ToDataURL method using canvas

**Draw to canvas: **Draw screenshot data onto a canvas element. First, create a new canvas element and set its size the same as the desired screenshot size. Then, use JavaScript to draw the screenshot data onto this canvas.

**Convert to data URL: **Use canvastoDataURLMethod converts the contents in canvas to a data URL. This method can convert image data in canvas into a base64-encoded string, represented as a URL.

**Create a download link: ** Assign the generated data URL to<a>TagshrefAttributes, set at the same timedownloadThe property is the required file name. The image file will be automatically downloaded when the user clicks on the link.

WeChat applet

If it is in a WeChat applet, because it is not html, the processing will be different. In WeChat applets, to implement the screenshot function, you can use the official applet provided by the appletinterface. This interface can convert the content in Canvas into a temporary file path, thereby implementing the screenshot function.

The specific steps are as follows:

  • Create a<canvas>element and draw the content that needs to be taken on this Canvas.
  • CallThe interface converts the contents in Canvas to temporary file paths.
  • After obtaining the temporary file path, you can perform subsequent operations, such as saving to the album, uploading to the server, etc.

As we can see above, since there are various ends, they may not necessarily support html or canvas, and the complete consistency of each device and end cannot be guaranteed, so the picture can be generated directly on the backend and the frontend downloads screenshots according to the link.

The Puppeteer library can be used to implement screenshots and screenshots in . Puppeteer is a library developed by Google that provides a high-level API to control browser behavior through Chromium or Chrome. Using Puppeteer, you can simulate the behavior of the browser and realize the function of screenshots and long pictures in the browser.

When using Puppeteer to implement screenshots and long pictures, the following points need to be paid attention to:

  • **Installing Puppeteer: **First, you need to install the Puppeteer library, which can be installed through npm:npm install puppeteer。
  • **Screen taking using Puppeteer: **Use the API provided by Puppeteer, you can open a web page directly in the browser and save the screenshot of the web page content as an image.
  • **Implementation of screenshots: **To implement the function of screening long pictures, you can simulate the scrolling of the page, and capture the content of different parts many times, and then splice the cut content into a long picture.
  • **Compatible with browsers and WeChat applets: **Puppeteer library is developed for the environment and cannot be used directly in browsers or WeChat applets. If you want to implement the functions of screenshots and screenshots in a browser or WeChat applet, you can consider using the aforementioned method of screenshots in the browser or the method of screenshots in the applet.

Puppeteer

The function of intercepting long images in Puppeteer is relatively complicated, because Puppeteer can only intercept the content of the current viewport by default and cannot directly intercept the content of the entire page. However, it can be achieved by simulating the scrolling of the page, intercepting the content of different parts many times, and then splicing the intercepted content into a long picture.

The following is a method to cut long images:

  • **Set viewport size: **First, you need to set the viewport size of the page to ensure that you can display all the content you want to intercept. Available()Method sets the width and height of the page.
  • **Mock page scrolling: **Simulate page scrolling by executing JavaScript code to gradually intercept different parts of the page. Available()Method to execute JavaScript code.
  • **Intercepting content multiple times: **In the process of simulated scrolling, use()Method intercepts the content of the current viewport and saves it as a picture.
  • **Split screenshot: **Style multiple captured pictures into a long picture. You can use third-party libraries to realize the function of picture stitching, such asmerge-img。

Here is a simple example code that demonstrates how to implement the function of intercepting long graphs in Puppeteer:

const puppeteer = require('puppeteer');
const mergeImg = require('merge-img');

(async () =&gt; {
  const browser = await ();
  const page = await ();

  await ({ width: 1200, height: 800 }); // Set the page viewport size
  await (''); // Open the page
  const chunks = []; //Storing intercepted image data
  const scrollHeight = await (() =&gt; {
    // Simulate page scrolling and return to the scrolling height of the page    const distance = 800; // The distance each time    let totalHeight = 0;
    const timer = setInterval(() =&gt; {
      (0, distance);
      totalHeight += distance;
      if (totalHeight &gt;= ) {
        clearInterval(timer);
      }
    }, 100);
    return ;
  });

  for (let i = 0; i &lt; scrollHeight; i += 800) {
    // Each time you scroll 800px, intercept the content of the current viewport and save it as a picture    const screenshot = await ({ clip: { x: 0, y: i, width: 1200, height: 800 } });
    (screenshot);
  }

  await ();

  //Split the pictures  const mergedImg = await mergeImg(chunks, { direction: true });

  // Save the spliced ​​long picture  await ('long_screenshot.png');
})();

In this example, we first set the page's viewport size to 1200x800, then open a page and simulate the scrolling of the page, 800px each time. During scrolling, multiple calls()Method intercepts the content of the current viewport and saves it as a picture. Finally, usemerge-imgThe library splices all the intercepted images into a long image and saves them locally.

It should be noted that this is just a simple example code, and in actual scenarios, it may need to be adjusted and optimized according to the specific situation of the page.

This is the end of this article about how to implement screenshot functions in JavaScript front-end. For more related JavaScript screenshot content, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!