Implementation of nodejs image paging

As the website develops, the number of pictures that need to be displayed is also increasing. If you blindly load all the images at once, it will not only affect the user experience, but also reduce the performance of the website. Therefore, the implementation of image paging is becoming more and more important.

This article will mainly introduce the method of using Node.js to implement image paging. Before that, let’s briefly introduce the principles and requirements of image paging.

The principle of picture paging

The principle of picture paging is very simple, that is, multiple pictures are divided into several pages for display, and users can browse these pictures through different page numbers. To implement, we only need to divide all pictures into several groups according to the number of pictures to be displayed on each page, and return the picture group corresponding to the page number according to the user's request.

Requirements for image paging

Before implementing image paging, we need to determine the actual requirements for better implementation. For example:

• What is the number of images displayed on each page?
• How to divide all pictures into how many pages? (How many pictures are there, how many pictures per page)
• How to get the page number requested by the user?
• How to preload images?

Next, this article will implement a simple image paging example through code to solve the above problems.

1. Implementation method

First, we need an image data source (in this example, an image in an npm package named "dog" is used). We use the fs module in Node.js to read the image, and use the express module to create the server and send the image to the client. The specific code is as follows:

// 引入依赖包和模块
const express = require('express')
const fs = require('fs')

const app = express()

app.get('/images/:page', (req, res) => {
  const imagesPerPage = 6 // 每页展示6张图片
  const page = req.params.page
  const start = (page - 1) * imagesPerPage // 初始图片位置
  const end = start + imagesPerPage // 结束图片位置

  // 读取所有图片，并将其分页
  fs.readdir(__dirname + '/images', (err, files) => {
    if (err) throw err

    const imageFiles = files.filter(file => {
      return /.(jpe?g|png|gif)$/i.test(file)
    })
    const totalPages = Math.ceil(imageFiles.length / imagesPerPage) // 计算总页数

    // 返回指定页码的图片
    res.send({
      images: imageFiles.slice(start, end),
      totalPages: totalPages
    })
  })
})

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000')
})

Run the program, then visit http://localhost:3000/images/1 in the browser to see 6 pictures displayed on each page, refresh the page or change "1" For other numbers, you can view pictures on other pages.

2. Implementing preloading

In order to optimize the user experience, when the user browses to a certain page, we need to start preloading the images of the next page. The specific code is as follows:

// 引入依赖包和模块
const express = require('express')
const fs = require('fs')

const app = express()

app.get('/images/:page', (req, res) => {
  const imagesPerPage = 6 // 每页展示6张图片
  const page = req.params.page
  const start = (page - 1) * imagesPerPage // 初始图片位置
  const end = start + imagesPerPage // 结束图片位置

  // 读取所有图片，并将其分页
  fs.readdir(__dirname + '/images', (err, files) => {
    if (err) throw err

    const imageFiles = files.filter(file => {
      return /.(jpe?g|png|gif)$/i.test(file)
    })
    const totalPages = Math.ceil(imageFiles.length / imagesPerPage) // 计算总页数

    // 计算下一页的页面地址
    const nextPage = parseInt(page) + 1
    const nextPageUrl = '/images/' + nextPage

    // 返回指定页码的图片及下一页的页面地址
    res.send({
      images: imageFiles.slice(start, end),
      totalPages: totalPages,
      nextPage: nextPageUrl
    })
  })
})

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000')
})

In the above code, we added the nextPageUrl variable to return the page address of the next page to the client. Use JavaScript on the client to download the address of nextPageUrl to preload the image of the next page.

3. Summary

This article introduces the method of using Node.js to realize image paging, and on this basis, realizes the preloading of images. In actual development, paging images is a common requirement. Mastering this set of implementation methods will help improve the development efficiency and user experience of the project.

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