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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.

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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.