joppot

コピペで絶対動く。説明を妥協しない

プログラミング

Lazy load image with react-lazyload

投稿日:2018年12月3日 更新日:


Abstract

Hello everyoen it’s me candle. This time let’s make a delayed loading of images with react-lazyload. The problem of SPA is the delay at the time of initial loading. Among them, we feel that the site with many images is even late. Let’s try it.

Condition

Nothing

Prepare

If you have already developing react project, use it.
But you don’t have yet or try to test. Generate it with this command.

create-react-app imageloader-sample
cd imageloader-sample

We will prepare images for samples with Faker.js, so install it.

yarn add faker

Ready to develop.

Make a sample code

Open the src/App.js and edit like this.

import React, { Component } from 'react'
import Faker from 'faker'

class App extends Component {
  constructor(props) {
    super(props)
    this.state = {
      users: [],
    }
  }
  componentWillMount() {
    for (let i = 0; i < 30; i++) {
      const user = {
        name: Faker.internet.userName(),
        email: Faker.internet.email(),
        avatar: Faker.internet.avatar(),
      }
      this.setState(prevState => ({
        users: [...prevState.users, user],
      }))
    }
  }

  renderUsers(user) {
    return (
      <div style={{ border: 'solid 1px #eee' }}>
        <img src={user.avatar} alt={user.name} width="50" height="50" />
        <h4>Name: {user.name}</h4>
        <h4>Email: {user.email}</h4>
      </div>
    )
  }

  render() {
    return <div>{this.state.users.map(user => this.renderUsers(user))}</div>
  }
}

export default App

Execute this code and you can see this screen.

It displays the thirty images on the screen.

Use React-lazyload

First we will install react-lazyload.

yarn add react-lazyload

Open the src/App.js and edit.

import React, { Component } from 'react'
import Faker from 'faker'

import LazyLoad from 'react-lazyload'

class App extends Component {
  constructor(props) {
    super(props)
    this.state = {
      users: [],
    }
  }
  componentWillMount() {
    for (let i = 0; i < 30; i++) {
      const user = {
        name: Faker.internet.userName(),
        email: Faker.internet.email(),
        avatar: Faker.internet.avatar(),
      }
      this.setState(prevState => ({
        users: [...prevState.users, user],
      }))
    }
  }

  renderUsers(user) {
    return (
      <div style={{ border: 'solid 1px #eee' }}>
        <LazyLoad width="50" height="50" once>
          <img src={user.avatar} alt={user.name} width="50" height="50" />
        </LazyLoad>
        <h4>Name: {user.name}</h4>
        <h4>Email: {user.email}</h4>
      </div>
    )
  }

  render() {
    return <div>{this.state.users.map(user => this.renderUsers(user))}</div>
  }
}

export default App

In this way, only the minimum required image is loaded, and the rest are loaded lazily.

It went good.

Conclusion

It is better to do lazy loading of images absolutely so let’s try it out.

スポンサードリンク

If you think this article is good, share it please

-プログラミング
-,

執筆者:


comment

Your email address will not be published. Required fields are marked *

関連記事

Remove or allow the html tag with javascript + React and take measures against XSS

Abstract Hello everyone it’s me candle. In this time, we will write a program which displays only the permitted html tags by React and delete other tags. Notice, displaying originally html contents, it may has a security risk such as XSS. First of all, I am not a security expert, so there is a possibility of a bug in the code. Of course, I check it and test it as long as I do. If you find any vulnerabilities in the code, it would be helpful if you point out it in the post comment form. Condition Nothing Preparation of …

How to change the language form “en-US” to “en” by wordpres bogo

English 日本語 Abstract Hello everyone, It’s me candle. In this time, I will show you to customize bogo plugins. The bogo is wonderful plugin which can adapt the wordpress site to many languages as a simple. but, there is a problem that you can’t choose general English. When writing English articles, you may not always have to write it limited to country. However, you can choose ‘en-UK’, ‘en-CA’ and ‘en-US’, but ‘en’ can not be chosen in bogo. I checked the source code. The bogo got a language list from wordpress function, and there is no general English in it. …

Create plantUML with emacs using plantuml-mode

Autumn leaves on wood table Abstract Hello everyone it’s me candle. In this time, we will introduce plantuml-mode of emacs supporting plantUML. plantuml-mode has three functions. Syntax highlight Autocomplete Display UML preview There are plenty of settings, so let’s do it patiently. Precondition You had plantuml command I installed plantuml with brew. but it is ok you prepare jar file. If you don’t have it yet, please refer to here. Build PlantUML environment on Mac using brew Install plantuml-mode The latest version of plant-mode is not yet registered in el-get packages, so we will get it from github directly. For …

I created docker shortcut command with bash alias

Abstract Hello everyone it’s me candle. I will introduce easy operation of the docker command. Of course, I just created it thinking that it was useful, so please change it for much more useful. Precondition You use bash. ( Even though you use zsh or csh or something else, you edit a bit, it will work well) You use docker

Using sphinx how to generate documents of python classes and functions

Abstruct Hello everyone it’s me candle. In this article I will explain how to make documents about classes and functions with Sphinx automatically. condition I will explain it using Python 3, but I think that it will probably work with python 2 as well. Prepare test files Create a main.py and dog.py. touch main.py dog.py Write this to the main.py from dog import Dog def main(): dog = Dog() dog.show_name() if __name__ == "__main__": main() Open the dog.py and write it. class Dog(object): def __init__(self, name="bob"): self.name = name def bark(): print("Bow Wow") def show_name(self): print(self.name) def get_name(self): return self.name …


I work in the venture company as a CTO. I start to write program in University, first I learned java, C++ and PHP. In the company, I'm developing web services by Rails. I do like to automation.