Dane Stevens

Building the React Image Optimization Component for Tueri.io

March 21, 2019

Let’s face it, image optimization is hard. We want to make it effortless.

Full source code can be found on GitHub

When we set out to build our React Component there were a few problems we wanted to solve:

  • Automatically decide image width for any device based on the parent container.

  • Use the best possible image format the user’s browser supports.

  • Automatic image lazy loading.

  • Automatic low-quality image placeholders (LQIP).

Oh, and it had to be effortless for React Developers to use.

This is what we came up with:

<Img src={ tueriImageId } alt='Alt Text' />

Easy right? Let’s dive in.

Calculating the image size:

Create a <figure /> element, detect the width and build an image URL:

class Img extends React.Component {

    constructor(props) {
        super(props)
        this.state = {
            width: 0
        }
        this.imgRef = React.createRef()
    }

    componentDidMount() {
        const width = this.imgRef.current.clientWidth
        this.setState({
            width
        })
    }

    render() {

        // Destructure props and state
        const { src, alt, options = {}, ext = 'jpg' } = this.props
        const { width } = this.state

        // Create an empty query string
        let queryString = ''        

        // If width is specified, otherwise use auto-detected width
        options['w'] = options['w'] || width

        // Loop through option object and build queryString
        Object.keys(options).map((option, i) => {
            return queryString +=  `${i < 1 ? '?' : '&'}${option}=${options[option]}`
        })

        return(
            <figure ref={this.imgRef}>
                { 
                    // If the container width has been set, display the image else null
                    width > 0 ? (
                        <img
                            src={`https://cdn.tueri.io/${ src }/${ kebabCase(alt) }.${ ext }${ queryString }`}
                            alt={ alt }
                        />
                    ) : null 
                }
            </figure>
        )

    }
}

export default Img

This returns the following HTML:

<figure>
    <img 
        src="https://cdn.tueri.io/tueriImageId/alt-text.jpg?w=autoCalculatedWidth" 
        alt="Alt Text" 
    />
</figure>

Use the best possible image format:

Next, we needed to add support for detecting WebP images and having the Tueri service return the image in the WebP format:

class Img extends React.Component {

    constructor(props) {
        // ...
        this.window = typeof window !== 'undefined' && window
        this.isWebpSupported = this.isWebpSupported.bind(this)
    }

    // ...
    
    isWebpSupported() {
        if (!this.window.createImageBitmap) {
            return false;
        }
        return true;
    }

    render() {

        // ...

        // If a format has not been specified, detect webp support
        // Set the fm (format) option in the image URL
        if (!options['fm'] && this.isWebpSupported) {
            options['fm'] = 'webp'
        }

        // ...
        
        return (
            // ...
        )

    }
}

// ...

This returns the following HTML:

<figure>
    <img 
        src="https://cdn.tueri.io/tueriImageId/alt-text.jpg?w=autoCalculatedWidth&fm=webp" 
        alt="Alt Text" 
    />
</figure>

Automatic image lazy loading:

Now, we need to find out if the <figure /> element is in the viewport, plus we add a little buffer area so the images load just before being scrolled into view.

   class Img extends React.Component {

   constructor(props) {
       // ...
       this.state = {
           // ...
           isInViewport: false
           lqipLoaded: false
       }
       // ...
       this.handleViewport = this.handleViewport.bind(this)
   }

   componentDidMount() {
       // ...
       this.handleViewport()
       this.window.addEventListener('scroll', this.handleViewport)
   }
   
   handleViewport() {
       // Only run if the image has not already been loaded
       if (this.imgRef.current && !this.state.lqipLoaded) {
           // Get the viewport height
           const windowHeight = this.window.innerHeight
           // Get the top position of the <figure /> element
           const imageTopPosition = this.imgRef.current.getBoundingClientRect().top
           // Multiply the viewport * buffer (default buffer: 1.5)
           const buffer = typeof this.props.buffer === 'number' && this.props.buffer > 1 && this.props.buffer < 10 ? this.props.buffer : 1.5
           // If <figure /> is in viewport
           if (windowHeight * buffer > imageTopPosition) {
               this.setState({
                   isInViewport: true
               })
           }
       }
   }
   
   // ...
   
   componentWillUnmount() {
       this.window.removeEventListener('scroll', this.handleViewport)
   }

   render() {

       // Destructure props and state
       // ...
       const { isInViewport, width } = this.state
       
       // ...
       
       return (
           <figure ref={this.imgRef}>
               { 
                   // If the container width has been set, display the image else null
                   isInViewport && width > 0 ? (
                       <img 
                           onLoad={ () => { this.setState({ lqipLoaded: true }) } }
                           // ...
                       />
                   ) : null 
               }
           </figure>
       )

   }
}

export default Img

Automatic low-quality image placeholders (LQIP):

Finally, when an image is in the viewport, we want to load a 1/10 size blurred image, then fade out the placeholder image when the full-size image is loaded:

class Img extends React.Component {

    constructor(props) {
        // ...
        this.state = {
            // ...
            fullsizeLoaded: false
        }

        // ...

    }

    // ...

    render() {

        // Destructure props and state
        // ...
        const { isInViewport, width, fullsizeLoaded } = this.state

        // ...
        
        // Modify the queryString for the LQIP image: replace the width param with a value 1/10 the fullsize
        const lqipQueryString = queryString.replace(`w=${ width }`, `w=${ Math.round(width * 0.1) }`)

        // Set the default styles. The full size image should be absolutely positioned within the <figure /> element
        const styles = {
            figure: {
                position: 'relative',
                margin: 0
            },
            lqip: {
                width: '100%',
                filter: 'blur(5px)',
                opacity: 1,
                transition: 'all 0.5s ease-in'
            },
            fullsize: {
                position: 'absolute',
                top: '0px',
                left: '0px',
                transition: 'all 0.5s ease-in'
            }
        }

        // When the fullsize image is loaded, fade out the LQIP
        if (fullsizeLoaded) {
            styles.lqip.opacity = 0
        }

        return(
            <figure
                style={ styles.figure }
                // ...
            >
                {
                    isInViewport && width > 0 ? (
                        <React.Fragment>

                            {/* Load fullsize image in background */}
                            <img 
                                onLoad={ () => { this.setState({ fullsizeLoaded: true }) } }
                                style={ styles.fullsize }
                                src={`https://cdn.tueri.io/${ src }/${ kebabCase(alt) }.${ ext }${ queryString }`}
                                alt={ alt }
                            />

                            {/* Load LQIP in foreground */}
                            <img 
                                onLoad={ () => { this.setState({ lqipLoaded: true }) } }
                                style={ styles.lqip }
                                src={`https://cdn.tueri.io/${ src }/${ kebabCase(alt) }.${ ext }${ lqipQueryString }`} 
                                alt={ alt } 
                            />
                        </React.Fragment>
                    ) : null
                }            
            </figure>
        )

    }
}

// ...

Putting it all together:

Image optimization made effortless. Just swap out your regular <img /> elements for the Tueri <Img /> and never worry about optimization again.

import React from 'react'
import PropTypes from 'prop-types'
import { TueriContext } from './Provider'
import kebabCase from 'lodash.kebabcase'

class Img extends React.Component {

    constructor(props) {
        super(props)
        this.state = {
            isInViewport: false,
            width: 0,
            height: 0,
            lqipLoaded: false,
            fullsizeLoaded: false
        }

        this.imgRef = React.createRef()
        this.window = typeof window !== 'undefined' && window 
        this.handleViewport = this.handleViewport.bind(this)       
        this.isWebpSupported = this.isWebpSupported.bind(this)

    }

    componentDidMount() {

        const width = this.imgRef.current.clientWidth

        this.setState({
            width
        })
        
        this.handleViewport()

        this.window.addEventListener('scroll', this.handleViewport)

    }

    handleViewport() {
        if (this.imgRef.current && !this.state.lqipLoaded) {
            const windowHeight = this.window.innerHeight
            const imageTopPosition = this.imgRef.current.getBoundingClientRect().top
            const buffer = typeof this.props.buffer === 'number' && this.props.buffer > 1 && this.props.buffer < 10 ? this.props.buffer : 1.5
            if (windowHeight * buffer > imageTopPosition) {
                this.setState({
                    isInViewport: true
                })
            }

        }
    }

    isWebpSupported() {
        if (!this.window.createImageBitmap) {
            return false;
        }
        return true;
    }

    componentWillUnmount() {
        this.window.removeEventListener('scroll', this.handleViewport)
    }

    render() {

        // Destructure props and state
        const { src, alt, options = {}, ext = 'jpg' } = this.props
        const { isInViewport, width, fullsizeLoaded } = this.state

        // Create an empty query string
        let queryString = ''

        // If width is specified, otherwise use auto-detected width
        options['w'] = options['w'] || width

        // If a format has not been specified, detect webp support
        if (!options['fm'] && this.isWebpSupported) {
            options['fm'] = 'webp'
        }

        // Loop through option prop and build queryString
        Object.keys(options).map((option, i) => {
            return queryString +=  `${i < 1 ? '?' : '&'}${option}=${options[option]}`
        })

        // Modify the queryString for the LQIP image: replace the width param with a value 1/10 the fullsize
        const lqipQueryString = queryString.replace(`w=${ width }`, `w=${ Math.round(width * 0.1) }`)

        const styles = {
            figure: {
                position: 'relative',
                margin: 0
            },
            lqip: {
                width: '100%',
                filter: 'blur(5px)',
                opacity: 1,
                transition: 'all 0.5s ease-in'
            },
            fullsize: {
                position: 'absolute',
                top: '0px',
                left: '0px',
                transition: 'all 0.5s ease-in'
            }
        }

        // When the fullsize image is loaded, fade out the LQIP
        if (fullsizeLoaded) {
            styles.lqip.opacity = 0
        }

        const missingALt = 'ALT TEXT IS REQUIRED'

        return(
            // Return the CDN domain from the TueriProvider
            <TueriContext.Consumer>
                {({ domain }) => (
                    <figure
                        style={ styles.figure }
                        ref={this.imgRef}
                    >
                        {
                            // 
                            isInViewport && width > 0 ? (
                                <React.Fragment>

                                    {/* Load fullsize image in background */}
                                    <img 
                                        onLoad={ () => { this.setState({ fullsizeLoaded: true }) } }
                                        style={ styles.fullsize }
                                        src={`${ domain }/${ src }/${ kebabCase(alt || missingALt) }.${ ext }${ queryString }`}
                                        alt={ alt || missingALt }
                                    />

                                    {/* Load LQIP in foreground */}
                                    <img 
                                        onLoad={ () => { this.setState({ lqipLoaded: true }) } }
                                        style={ styles.lqip }
                                        src={`${ domain }/${ src }/${ kebabCase(alt || missingALt) }.${ ext }${ lqipQueryString }`} 
                                        alt={ alt || missingALt } 
                                    />
                                </React.Fragment>
                            ) : null
                        }            
                    </figure>
                )}
                
            </TueriContext.Consumer>
        )

    }
}

Img.propTypes = {
    src: PropTypes.string.isRequired,
    alt: PropTypes.string.isRequired,
    options: PropTypes.object,
    ext: PropTypes.string,
    buffer: PropTypes.number
}

export default Img

See it in action:

Try out a live demo on CodeSandbox:

Originally published at Tueri.io


Dane Stevens

A blog by Dane Stevens. Founder at Tueri.io