gatsby-background-image-es5-preact

v1.1.2-alpha.1

Published

3 years ago

(preact-fork) Lazy-loading React background-image component with optional support for the blur-up effect. Transpiled to ES5.

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jaredhenderson

gatsby gastby-component gatsby-image background-image backgroundImage background image react-component ES5

gatsby-background-image-es5 is a React component which for background-images provides,
what Gatsby's own gatsby-image does for the rest of your images.

Preamble

This version is completely transpiled to ES5 to target older browsers like IE11! Most polyfills are already built in, though this nearly triples the package size compared to gatsby-background-image!

Everything else just works the same as in gatsby-background-image, so it provides for background-images, what Gatsby's own gatsby-image does for the rest of your images and even more:
Testing explained in its own section. Art-Direction support built in.

It has all the advantages of gatsby-image, including the "blur-up" technique or a "traced placeholder" SVG to show a preview of the image while it loads,
plus being usable as a container (no more hacks with extra wrappers)
plus being able to work with multiple stacked background images
plus being able to style with Tailwind CSS and suchlike Frameworks

All the glamour (and speed) of gatsby-image for your Background Images!

Of course styleable with styled-components and the like!

Example Repo

gatsby-background-image has an example repository to see its similarities & differences to gatsby-image side by side.
It's located at: gbitest To use it with gatsby-background-image-es5 change the dependency there.

Procedure

As gatsby-image is designed to work seamlessly with Gatsby's native image processing capabilities powered by GraphQL and Sharp, so is gatsby-background-image-es5. To produce optimized background-images, you need only to:

Import gatsby-background-image-es5 and use it in place of the built-in div or suchlike containers.
Write a GraphQL query using one of the GraphQL "fragments" provided by gatsby-transformer-sharp
which specify the fields needed by gatsby-background-image-es5.

The GraphQL query creates multiple thumbnails with optimized JPEG and PNG compression (or even WebP files for browsers that support them). The gatsby-background-image-es5 component automatically sets up the "blur-up" effect as well as lazy loading of images further down the screen.

Install

To add gatsby-background-image-es5 as a dependency to your Gatsby-project use

npm install --save gatsby-background-image-es5

yarn add gatsby-background-image-es5

Depending on the gatsby starter you used, you may need to include gatsby-transformer-sharp and gatsby-plugin-sharp as well, and make sure they are installed and included in your gatsby-config.

npm install --save gatsby-transformer-sharp gatsby-plugin-sharp

yarn add gatsby-transformer-sharp gatsby-plugin-sharp

Then in your gatsby-config.js:

plugins: [`gatsby-transformer-sharp`, `gatsby-plugin-sharp`]

Also, make sure you have set up a source plugin, so your images are available in graphql queries. For example, if your images live in a project folder on the local filesystem, you would set up gatsby-source-filesystem in gatsby-config.js like so:

const path = require(`path`)

module.exports = {
  plugins: [
    {
      resolve: `gatsby-source-filesystem`,
      options: {
        name: `images`,
        path: path.join(__dirname, `src`, `images`),
      },
    },
    `gatsby-plugin-sharp`,
    `gatsby-transformer-sharp`,
  ],
}

Tailwind CSS and suchlike Frameworks

With gatsby-background-image(-es5) @ v0.8.8 it's now possible to use Tailwind CSS classes like md:w-1/2 to style BackgroundImage. Therefore a specialChars plugin option has been introduced to be able to properly escape such classes, which defaults to :/ but may be set to other characters in gatsby-config.js like the following:

module.exports = {
  plugins: [
    ...
    {
      resolve: 'gatsby-background-image-es5',
      options: {
        // add your own characters to escape, replacing the default ':/'
        specialChars: '/:',
      },
    },
    ...
   ],
};

Important:

If you support Safari and/or Internet Explorer, you have to use the IntersectionObserver polyfill.
As - at the time of writing - neither fully implements the feature (see caniuse.com).

This is already the ES5 version of gatsby-background-image, so nothing easier than that! Just add gatsby-background-image-es5 as a plugin to your gatsby-config.js like this:

module.exports = {
  plugins: [
    ...
    `gatsby-background-image-es5`,
    ...
]

And

How to Use

Be sure to play around with the Example Repo, as it shows a few more flavors of using BackgroundImage, e.g. encapsulating it in a component : )!

This is what a component using gatsby-background-image-es5 might look like:

import React from 'react'
import { graphql, useStaticQuery } from 'gatsby'
import styled from 'styled-components'

import BackgroundImage from 'gatsby-background-image-es5'

const BackgroundSection = ({ className }) => {
  const data = useStaticQuery(
    graphql`
      query {
        desktop: file(relativePath: { eq: "seamless-bg-desktop.jpg" }) {
          childImageSharp {
            fluid(quality: 90, maxWidth: 1920) {
              ...GatsbyImageSharpFluid_withWebp
            }
          }
        }
      }
    `
  )

  // Set ImageData.
  const imageData = data.desktop.childImageSharp.fluid

  return (
    <BackgroundImage
      Tag="section"
      className={className}
      fluid={imageData}
      backgroundColor={`#040e18`}
    >
      <h2>gatsby-background-image</h2>
    </BackgroundImage>
  )
}

const StyledBackgroundSection = styled(BackgroundSection)`
  width: 100%;
  background-position: bottom center;
  background-repeat: repeat-y;
  background-size: cover;
`

export default StyledBackgroundSection

And here is the same component with the data retrieved the old way with the StaticQuery component:

import React from 'react'
import { graphql, StaticQuery } from 'gatsby'
import styled from 'styled-components'

import BackgroundImage from 'gatsby-background-image-es5'

const BackgroundSection = ({ className }) => (
  <StaticQuery
    query={graphql`
      query {
        desktop: file(relativePath: { eq: "seamless-bg-desktop.jpg" }) {
          childImageSharp {
            fluid(quality: 90, maxWidth: 1920) {
              ...GatsbyImageSharpFluid_withWebp
            }
          }
        }
      }
    `}
    render={data => {
      // Set ImageData.
      const imageData = data.desktop.childImageSharp.fluid
      return (
        <BackgroundImage
          Tag="section"
          className={className}
          fluid={imageData}
          backgroundColor={`#040e18`}
        >
          <h2>gatsby-background-image-es5</h2>
        </BackgroundImage>
      )
    }}
  />
)

const StyledBackgroundSection = styled(BackgroundSection)`
  width: 100%;
  background-position: bottom center;
  background-repeat: repeat-y;
  background-size: cover;
`

export default StyledBackgroundSection

How to Use with Multiple Images

As gatsby-background-image may be used with multiple backgrounds, including CSS strings like rgba() or suchlike this is what a component using gatsby-background-image-es5 might look like:

import { graphql, useStaticQuery } from 'gatsby'
import React from 'react'
import styled from 'styled-components'

import BackgroundImage from 'gatsby-background-image-es5'

const MultiBackground = ({ children, className }) => {
  const {
    astronaut,
    seamlessBackground,
  } = useStaticQuery(
    graphql`
      query {
        astronaut: file(relativePath: { eq: "astronaut.png" }) {
          childImageSharp {
            fluid(quality: 100) {
              ...GatsbyImageSharpFluid_withWebp
            }
          }
        }
        seamlessBackground: file(
          relativePath: { eq: "seamless-background.jpg" }
        ) {
          childImageSharp {
            fluid(quality: 100, maxWidth: 420) {
              ...GatsbyImageSharpFluid_withWebp
            }
          }
        }
      }
    `
  )

  // Watch out for CSS's stacking order, especially when styling the
  // individual positions! The lowermost image comes last!
  const backgroundFluidImageStack = [
    seamlessBackground.childImageSharp.fluid,
    `linear-gradient(rgba(220, 15, 15, 0.73), rgba(4, 243, 67, 0.73))`
    astronaut.childImageSharp.fluid,
  ].reverse()

  return (
    <BackgroundImage
      Tag={`section`}
      id={`test`}
      className={className}
      fluid={backgroundFluidImageStack}
    >
      <StyledInnerWrapper>
        <h2>
          This is a test of multiple background images.
        </h2>
      </StyledInnerWrapper>
    </BackgroundImage>
  )
}

const StyledInnerWrapper = styled.div`
  margin-top: 10%;
  display: flex;
  flex-direction: column;
  align-items: center;
`

const StyledMultiBackground = styled(MultiBackground)`
  width: 100%;
  min-height: 100vh;
  /* You should set a background-size as the default value is "cover"! */
  background-size: auto;
  /* So we won't have the default "lightgray" background-color. */
  background-color: transparent;
  /* Now again, remember the stacking order of CSS: lowermost comes last! */
  background-repeat: no-repeat, no-repeat, repeat;
  background-position: center 155%, center, center;
  color: #fff;
`

export default StyledMultiBackground

How to Use with Art-Direction support

gatsby-background-image-es5 supports showing different images at different breakpoints, which is known as art direction. To do this, you can define your own array of fixed or fluid images, along with a media key per image, and pass it to gatsby-image's fixed or fluid props. The media key that is set on an image can be any valid CSS media query.

Attention: Currently you have to choose between Art-directed and Multiple-Images!

import { graphql, useStaticQuery } from 'gatsby'
import React from 'react'
import styled from 'styled-components'

import BackgroundImage from 'gatsby-background-image-es5'

const ArtDirectedBackground = ({ className }) => {
  const { mobileImage, desktopImage } = useStaticQuery(
    graphql`
      query {
        mobileImage: file(relativePath: { eq: "490x352.jpg" }) {
          childImageSharp {
            fluid(maxWidth: 490, quality: 100) {
              ...GatsbyImageSharpFluid_withWebp
            }
          }
        }
        desktopImage: file(relativePath: { eq: "tree.jpg" }) {
          childImageSharp {
            fluid(quality: 100, maxWidth: 4160) {
              ...GatsbyImageSharpFluid_withWebp
            }
          }
        }
      }
    `
  )
  // Set up the array of image data and `media` keys.
  // You can have as many entries as you'd like.
  const sources = [
    mobileImage.childImageSharp.fluid,
    {
      ...desktopImage.childImageSharp.fluid,
      media: `(min-width: 491px)`,
    },
  ]

  return (
    <BackgroundImage
      Tag={`section`}
      id={`media-test`}
      className={className}
      fluid={sources}
    >
      <StyledInnerWrapper>
        <h2>Hello art-directed gatsby-background-image.</h2>
      </StyledInnerWrapper>
    </BackgroundImage>
  )
}

const StyledInnerWrapper = styled.div`
  margin-top: 10%;
  display: flex;
  flex-direction: column;
  align-items: center;
`

const StyledArtDirectedBackground = styled(ArtDirectedBackground)`
  width: 100%;
  min-height: 100vh;
  /* You should set a background-size as the default value is "cover"! */
  background-size: auto;
  /* So we won't have the default "lightgray" background-color. */
  background-color: transparent;
`

export default StyledArtDirectedBackground

While you could achieve a similar effect with plain CSS media queries, gatsby-background-image-es5 accomplishes this using an internal HTMLPictureElement, as well as window.matchMedia(), which ensures that browsers only download the image they need for a given breakpoint while preventing gatsby-image issue #15189.

Configuration & props

gatsby-background-image nearly works the same as gatsby-image so have a look at their options & props to get started. But be sure to also throw a glance at Additional props, Changed props, props Not Available and Handling of Remaining props as well ; )!

Styling & Passed Through Styles

You may style your gatsby-background-image-es5 BackgroundImage-component every way you like, be it global CSS, CSS-Modules or even with styled-components or your CSS-in-JS "framework" of choice. The style={{}} prop is supported as well.

Whichever way you choose, every background-* style declared in the main class (or the style={{}} prop) will directly get passed through to the pseudo-elements as well (so you would have no need for specifically styling them)!

The specificity hereby is in ascending order:

class-styles
extracted background-* styles
style={{}} prop

The three background- styles seen above are necessary and will default to:

| Name | Default Value | | --------------------- | ------------- | | background-position | center | | background-repeat | no-repeat | | background-size | cover |

To be able to overwrite them for each pseudo-element individually, you may reset their values in the style={{}} prop with an empty string like such:

style={{
  // Defaults are overwrite-able by setting one or each of the following:
  backgroundSize: '',
  backgroundPosition: '',
  backgroundRepeat: '',
}}

¡But be sure to target the :before and :after pseudo-elements in your CSS, lest your "blurred-up", traced placeholder SVG or lazy loaded background images might jump around!

Passed Props for styled-components and suchlike

Perhaps you want to change the style of a BackgroundImage by passing a prop to styled-components or suchlike CSS-in-JS libraries like e.g. the following:

// isDarken gets changed in the parent component.
const StyledBackground = styled(BackgroundImage)`
  &::before,
  &::after {
    filter: invert(
      ${({ isDarken }) => {
        return isDarken ? '80%' : '0%'
      }}
    );
  }
`

But be aware that there happens no state change inside the BackgroundImage, so React won't rerender it. This can easily be achieved, by settings an additional key prop, which changes as well as the prop like thus:

return <StyledBackgound isDarken={isDarken} key={isDarken ? `dark` : `light`} />

Overflow setting

As of gatsby-background-image(-es5) @ v0.8.3 the superfluous default of overflow: hidden was removed, as it was only a remnant from the initial creation of gbi (see Acknowledgements for more on its meagre beginnings ; ). As later seen through issue #59, this might break some CSS styling like border-radius, so be sure to include it yourself, should you need such styles. Sorry for the inconvenience % )!

Noscript Styling

As using multiple background images broke with JavaScript disabled, with v0.8.0 we switched to an added <style /> element.
Sadly, in build mode or of course with JS disabled there's no document with which to parse the background-styles from given classNames and pass them down to the :before and :after pseudo-elements.
So, for the moment, to get your <BackgroundImage /> to look the same with or without JS, you have to either set their styles with the style={{}} prop or explicitly target the :before and :after pseudo-elements in your CSS.

Responsive Styling

Using responsive styles on background images is supported in most cases, except when passthrough is required. This is typically encountered when trying to make background-* rules apply to the background image as in issue #71. In this case, the background styling will not behave responsively. This is difficult to fix because it is impossible to determine the @media rules that apply to an element. However, a suitable workaround is available. For example, if your style looks like this:

#mybg {
  background-attachment: fixed;
}
@media screen and (max-width: 600px) {
  #mybg {
    background-attachment: scroll;
  }
}

The ::before and ::after pseudoelements can be targeted directly to make your style look like this:

#mybg,
#mybg::before,
#mybg::after {
  background-attachment: fixed;
}

@media screen and (max-width: 600px) {
  #mybg,
  #mybg::before,
  #mybg::after {
    background-attachment: scroll;
  }
}

For more information, refer to issue #71.

Multiple Instances of Same Component

Should you decide to use a single instance of a styled <BackgroundImage /> for multiple different images, it will automatically add an additional className, a hashed 32bit integer of the current srcSet or className prefixed with gbi-, to prevent erroneous styling of individual instances.
You wouldn't have added the same class for different CSS background-image styles on your own, or would you have ; )?

Be warned: Styling the components :before & :after pseudo-elements within the main classes then only is going to work again for all instances if you use !important on its CSS-properties (cause of CSS-specifity).

Deprecated Styling

Though considered deprecated and to be removed in 1.0.0 at the latest (feel free to open an issue, should you really need them : ), gatsby-background-image-es5 has an added classId (as we had to name pseudo-elements and introduce a className for the returned container in the beginning):

| Name | Type | Description | | --------- | -------- | ------------------------------------------------------------------------------------------------------------ | | classId | string | classID of the container element, defaults to a random lower case string of seven chars, followed by _depr |

Only if present now, pseudo-elements are created on a class by the name of .gatsby-background-image-[YOUR_ID] and the class is added to BackgroundImage. Now you are able to access it through CSS / CSS-in-JS with:

.gatsby-background-image-[YOUR_ID]/*(:before, :after)*/ {
  background-repeat: repeat-y;
  background-position: bottom center;
  background-size: cover;
}

But as the paragraph-title states: This behavior is considered deprecated, so don't count on it in production ; ).

Additional props

Starting with v0.7.5 an extra option is available preserving the CSS stacking context by deactivating the "opacity hack (opacity: 0.99;)" used on <BackgroundImage /> to allow its usage within stacking context changing element styled with e.g. grid or flex per default.
Activating preserveStackingContext prevents this behavior - but allows you to use any stacking context changing elements (like elements styled with position: fixed;) yourself as children.

Starting with v0.8.19 it's possible to change the IntersectionObservers' rootMargin with a prop of the same name.

| Name | Type | Description | | ------------------------- | --------- | ------------------------------------------------------------------------------------------- | | preserveStackingContext | boolean | Deactivates the "opacity hack" on <BackgroundImage /> when set to true (Default: false) | | rootMargin | string | Changes the IntersectionObserver rootMargin. (Default: 200px) |

Changed props

The fluid or fixed props may be given as an array of images returned from fluid or fixed queries or CSS Strings like rgba() or such.

The fadeIn prop may be set to soft to ignore cached images and always try to fade in if critical isn't set.

| Name | Type | Description | | -------- | ------------------ | -------------------------------------------------------------------------------- | | fixed | object/array | Data returned from one fixed query or an array of multiple ones or CSS string(s) | | fluid | object/array | Data returned from one fluid query or an array of multiple ones or CSS string(s) | | fadeIn | boolean/string | Defaults to fading in the image on load, may be forced by soft |

props Not Available

As gatsby-background-image doesn't use placeholder-images, the following props from gatsby-image are not available, of course.

| Name | Type | Old Usage | | ---------------------- | -------- | ------------------------------------------------------------- | | placeholderStyle | object | Spread into the default styles of the placeholder img element | | placeholderClassName | string | A class that is passed to the placeholder img element | | imgStyle | object | Spread into the default styles of the actual img element |

In the absence of the placeholderStyle prop, additional styling while the image is loading can be accomplished using the onLoad or onStartLoad props. Use either method's callback to toggle a className on the component with your loading styles.

An example of "softening" the blur up using vanilla CSS.

/* MyBackgroundImage.css */

.loading,
.loading::before,
.loading::after {
  filter: blur(15px);
}

/* ...other styles */

// MyBackroundImage.js

import React, { useRef } from "react"
import BackgroundImage from "gatsby-background-image-es5"
import "./MyBackgroundImage.css"

const MyBackgroundImage = ({ children, ...props }) => {
  const bgRef = useRef()
  return (
    <BackgroundImage
      ref={bgRef}
      onStartLoad={() => bgRef.current.selfRef.classList.toggle("loading")}
      onLoad={() => bgRef.current.selfRef.classList.toggle("loading")}
      {...props}
    >
      {children}
    </BackgroundImage>
  )
}

export default MyBackgroundImage

For the same implementation with styled components, refer to #110.

From gbi v1.0.0 on the even older resolutions & sizes props are removed as well - but don't confuse the latter with the possible sizes image prop in a fluid image, which of course is still handled.

Handling of Remaining props

After every available prop is handled, the remaining ones get cleaned up and spread into the <BackgroundImage />'s container element. This way you can "safely" add every ARIA or data-* attribute you might need without having to use gatsby-image's itemProp ; ).

Testing `gatsby-background-image`

As gbi uses short-uuid to create its unique classes, you only have to mock short-uuid's generate() function like explained below.

Either in your jest.setup.js or the top of your individual test file(s) mock the complete package: jest.mock('short-uuid')

Then for each gbi component you want to test, add a beforeEach():

beforeEach(() => {
  // Freeze the generated className.
  const uuid = require('short-uuid')
  uuid.generate.mockImplementation(() => '73WakrfVbNJBaAmhQtEeDv')
});

Now the class name will always be the same and your snapshot tests should work : ).

Contributing

Everyone is more than welcome to contribute to this little package!
Docs, Reviews, Testing, Code - whatever you want to add, just go for it : ). So have a look at our CONTRIBUTING file and give it a go. Thanks in advance!

TODO

For anything you may think necessary tell me by opening an issue or a PR : )!

Acknowledgements

This package started by pilfering gatsby-images excellent work and adapting it - but it's definitely outgrowing those wee beginnings.
Thanks go to its creators & the @gatsbyjs Team, anyways : )!