@artsy/fresnel

The Fresnel equations describe the reflection of light when incident on an interface between different optical media.

– https://en.wikipedia.org/wiki/Fresnel_equations

Installation

  yarn add @artsy/fresnel

Table of Contents

Overview
Basic Example
Server-side Rendering (SSR)
Usage with Gatsby or Next
Example Apps
Why not conditionally render?
API
Pros vs Cons
Development

Overview

When writing responsive components it's common to use media queries to adjust the display when certain conditions are met. Historically this has taken place directly in CSS/HTML:

@media screen and (max-width: 767px) {
  .my-container {
    width: 100%;
  }
}
@media screen and (min-width: 768px) {
  .my-container {
    width: 50%;
  }
}

<div class="my-container" />

By hooking into a breakpoint definition, @artsy/fresnel takes this declarative approach and brings it into the React world.

Basic Example

import React from "react"
import ReactDOM from "react-dom"
import { createMedia } from "@artsy/fresnel"

const { MediaContextProvider, Media } = createMedia({
  // breakpoints values can be either strings or integers
  breakpoints: {
    sm: 0,
    md: 768,
    lg: 1024,
    xl: 1192,
  },
})

const App = () => (
  <MediaContextProvider>
    <Media at="sm">
      <MobileApp />
    </Media>
    <Media at="md">
      <TabletApp />
    </Media>
    <Media greaterThanOrEqual="lg">
      <DesktopApp />
    </Media>
  </MediaContextProvider>
)

ReactDOM.render(<App />, document.getElementById("react"))

Server-side Rendering (SSR) Usage

The first important thing to note is that when server-rendering with @artsy/fresnel, all breakpoints get rendered by the server. Each Media component is wrapped by plain CSS that will only show that breakpoint if it matches the user's current browser size. This means that the client can accurately start rendering the HTML/CSS while it receives the markup, which is long before the React application has booted. This improves perceived performance for end-users.

Why not just render the one that the current device needs? We can't accurately identify which breakpoint your device needs on the server. We could use a library to sniff the browser user-agent, but those aren't always accurate, and they wouldn't give us all the information we need to know when we are server-rendering. Once client-side JS boots and React attaches, it simply washes over the DOM and removes markup that is unneeded, via a matchMedia call.

SSR Example

First, configure @artsy/fresnel in a Media file that can be shared across the app:

// Media.tsx

import { createMedia } from "@artsy/fresnel"

const ExampleAppMedia = createMedia({
  breakpoints: {
    sm: 0,
    md: 768,
    lg: 1024,
    xl: 1192,
  },
})

// Generate CSS to be injected into the head
export const mediaStyle = ExampleAppMedia.createMediaStyle()
export const { Media, MediaContextProvider } = ExampleAppMedia

Create a new App file which will be the launching point for our application:

// App.tsx

import React from "react"
import { Media, MediaContextProvider } from "./Media"

export const App = () => {
  return (
    <MediaContextProvider>
      <Media at="sm">Hello mobile!</Media>
      <Media greaterThan="sm">Hello desktop!</Media>
    </MediaContextProvider>
  )
}

Mount <App /> on the client:

// client.tsx

import React from "react"
import ReactDOM from "react-dom"
import { App } from "./App"

ReactDOM.render(<App />, document.getElementById("react"))

Then on the server, setup SSR rendering and pass mediaStyle into a <style> tag in the header:

// server.tsx

import React from "react"
import ReactDOMServer from "react-dom/server"
import express from "express"

import { App } from "./App"
import { mediaStyle } from "./Media"

const app = express()

app.get("/", (_req, res) => {
  const html = ReactDOMServer.renderToString(<App />)

  res.send(`
    <html>
      <head>
        <title>@artsy/fresnel - SSR Example</title>

        <!–– Inject the generated styles into the page head -->
        <style type="text/css">${mediaStyle}</style>
      </head>
      <body>
        <div id="react">${html}</div>

        <script src='/assets/app.js'></script>
      </body>
    </html>
  `)
})

app.listen(3000, () => {
  console.warn("\nApp started at http://localhost:3000 \n")
})

And that's it! To test, disable JS and scale your browser window down to a mobile size and reload; it will correctly render the mobile layout without the need to use a user-agent or other server-side "hints".

Usage with Gatsby or Next

@artsy/fresnel works great with Gatsby or Next.js's static hybrid approach to rendering. See the examples below for a simple implementation.

Example Apps

There are four examples one can explore in the /examples folder:

While the Basic and SSR examples will get one pretty far, @artsy/fresnel can do a lot more. For an exhaustive deep-dive into its features, check out the Kitchen Sink app.

If you're using Gatsby, you can also try gatsby-plugin-fresnel for easy configuration.

Why not conditionally render?

Other existing solutions take a conditionally rendered approach, such as react-responsive or react-media, so where does this approach differ?

Server side rendering!

But first, what is conditional rendering?

In the React ecosystem a common approach to writing declarative responsive components is to use the browser’s matchMedia api:

<Responsive>
  {({ sm }) => {
    if (sm) {
      return <MobileApp />
    } else {
      return <DesktopApp />
    }
  }}
</Responsive>

On the client, when a given breakpoint is matched React conditionally renders a tree.

However, this approach has some limitations for what we wanted to achieve with our server-side rendering setup:

It's impossible to reliably know the user's current breakpoint during the server render phase since that requires a browser.
Setting breakpoint sizes based on user-agent sniffing is prone to errors due the inability to precisely match device capabilities to size. One mobile device might have greater pixel density than another, a mobile device may fit multiple breakpoints when taking device orientation into consideration, and on desktop clients there is no way to know at all. The best devs can do is guess the current breakpoint and populate <Responsive> with assumed state.

Artsy settled on what we think makes the best trade-offs. We approach this problem in the following way:

Render markup for all breakpoints on the server and send it down the wire.
The browser receives markup with proper media query styling and will immediately start rendering the expected visual result for whatever viewport width the browser is at.
When all JS has loaded and React starts the rehydration phase, we query the browser for what breakpoint it’s currently at and then limit the rendered components to the matching media queries. This prevents life-cycle methods from firing in hidden components and unused html being re-written to the DOM.
Additionally, we register event listeners with the browser to notify the MediaContextProvider when a different breakpoint is matched and then re-render the tree using the new value for the onlyMatch prop.

Let’s compare what a component tree using matchMedia would look like with our approach:

Before	After
<Responsive> {({ sm }) => { if (sm) return <SmallArticleItem {...props} /> else return <LargeArticleItem {...props} /> }} </Responsive>	<> <Media at="sm"> <SmallArticleItem {...props} /> </Media> <Media greaterThan="sm"> <LargeArticleItem {...props} /> </Media> </>

Before

After

<Responsive>
  {({ sm }) => {
    if (sm) return <SmallArticleItem {...props} />
    else return <LargeArticleItem {...props} />
  }}
</Responsive>

<>
  <Media at="sm">
    <SmallArticleItem {...props} />
  </Media>
  <Media greaterThan="sm">
    <LargeArticleItem {...props} />
  </Media>
</>

See the server-side rendering app for a working example.

API

createMedia

First things first. You’ll need to define the breakpoints and interaction needed for your design to produce the set of media components you can use throughout your application.

For example, consider an application that has the following breakpoints:

A viewport width between 0 and 768 (768 not included) points, named sm.
A viewport width between 768 and 1024 (1024 not included) points, named md.
A viewport width between 1024 and 1192 (1192 not included) points, named lg.
A viewport width from 1192 points and above, named xl.

And the following interactions:

A device that supports hovering a pointer device, named hover.
A device that does not support hovering a pointer device, named notHover.

You would then produce the set of media components like so:

// Media.tsx

const ExampleAppMedia = createMedia({
  breakpoints: {
    sm: 0,
    md: 768,
    lg: 1024,
    xl: 1192,
  },
  interactions: {
    hover: "(hover: hover)",
    notHover: "(hover: none)",
    landscape: "not all and (orientation: landscape)",
    portrait: "not all and (orientation: portrait)",
  },
})

export const { Media, MediaContextProvider, createMediaStyle } = ExampleAppMedia

As you can see, breakpoints are defined by their start offset, where the first one is expected to start at 0.

MediaContextProvider

The MediaContextProvider component influences how Media components will be rendered. Mount it at the root of your component tree:

import React from "react"
import { MediaContextProvider } from "./Media"

export const App = () => {
  return <MediaContextProvider>...</MediaContextProvider>
}

Media

The Media component created for your application has a few mutually exclusive props that make up the API you’ll use to declare your responsive layouts. These props all operate based on the named breakpoints that were provided when you created the media components.

import React from "react"
import { Media } from "./Media"

export const HomePage = () => {
  return (
    <>
      <Media at="sm">Hello mobile!</Media>
      <Media greaterThan="sm">Hello desktop!</Media>
    </>
  )
}

The examples given for each prop use breakpoint definitions as defined in the above ‘Setup’ section.

If you would like to avoid the underlying div that is generated by <Media> and instead use your own element, use the render-props form but be sure to not render any children when not necessary:

export const HomePage = () => {
  return (
    <>
      <Media at="sm">Hello mobile!</Media>
      <Media greaterThan="sm">
        {(mediaClassNames, renderChildren) => {
          return (
            <MySpecialComponent className={mediaClassNames}>
              {renderChildren ? "Hello desktop!" : null}
            </MySpecialComponent>
          )
        }}
      </Media>
    </>
  )
}

createMediaStyle

Note: This is only used when SSR rendering

Besides the Media and MediaContextProvider components, there's a createMediaStyle function that produces the CSS styling for all possible media queries that the Media instance can make use of while markup is being passed from the server to the client during hydration. If only a subset of breakpoint keys is used those can be optional specified as a parameter to minimize the output. Be sure to insert this within a <style> tag in your document’s <head>.

It’s advisable to do this setup in its own module so that it can be easily imported throughout your application:

import { createMedia } from "@artsy/fresnel"

const ExampleAppMedia = createMedia({
  breakpoints: {
    sm: 0,
    md: 768,
    lg: 1024,
    xl: 1192,
  },
})

// Generate CSS to be injected into the head
export const mediaStyle = ExampleAppMedia.createMediaStyle() // optional: .createMediaStyle(['at'])
export const { Media, MediaContextProvider } = ExampleAppMedia

onlyMatch

Rendering can be constrained to specific breakpoints/interactions by specifying a list of media queries to match. By default all will be rendered.

disableDynamicMediaQueries

By default, when rendered client-side, the browser’s matchMedia api will be used to further constrain the onlyMatch list to only the currently matching media queries. This is done to avoid triggering mount related life-cycle hooks of hidden components.

Disabling this behaviour is mostly intended for debugging purposes.

at

Use this to declare that children should only be visible at a specific breakpoint, meaning that the viewport width is greater than or equal to the start offset of the breakpoint, but less than the next breakpoint, if one exists.

For example, children of this Media declaration will only be visible if the viewport width is between 0 and 768 (768 not included) points:

<Media at="sm">...</Media>

The corresponding css rule:

@media not all and (min-width: 0px) and (max-width: 767px) {
  .fresnel-at-sm {
    display: none !important;
  }
}

lessThan

Use this to declare that children should only be visible while the viewport width is less than the start offset of the specified breakpoint.

For example, children of this Media declaration will only be visible if the viewport width is between 0 and 1024 (1024 not included) points:

<Media lessThan="lg">...</Media>

The corresponding css rule:

@media not all and (max-width: 1023px) {
  .fresnel-lessThan-lg {
    display: none !important;
  }
}

greaterThan

Use this to declare that children should only be visible while the viewport width is equal or greater than the start offset of the next breakpoint.

For example, children of this Media declaration will only be visible if the viewport width is equal or greater than 1024 points:

<Media greaterThan="md">...</Media>

The corresponding css rule:

@media not all and (min-width: 1024px) {
  .fresnel-greaterThan-md {
    display: none !important;
  }
}

greaterThanOrEqual

Use this to declare that children should only be visible while the viewport width is equal to the start offset of the specified breakpoint or greater.

For example, children of this Media declaration will only be visible if the viewport width is 768 points or up:

<Media greaterThanOrEqual="md">...</Media>

The corresponding css rule:

@media not all and (min-width: 768px) {
  .fresnel-greaterThanOrEqual-md {
    display: none !important;
  }
}

between

Use this to declare that children should only be visible while the viewport width is equal to the start offset of the first specified breakpoint but less than the start offset of the second specified breakpoint.

For example, children of this Media declaration will only be visible if the viewport width is between 768 and 1192 (1192 not included) points:

<Media between={["md", "xl"]}>...</Media>

The corresponding css rule:

@media not all and (min-width: 768px) and (max-width: 1191px) {
  .fresnel-between-md-xl {
    display: none !important;
  }
}

Pros vs Cons

Pros:

Built on top of simple, proven technology: HTML and CSS media queries.
Users see rendered markup at the correct breakpoint for their device, even before React has been loaded.

Cons:

If utilizing SSR rendering features, when the markup is passed down from the server to the client it includes all breakpoints, which increases the page size. (However, once the client mounts, the unused breakpoint markup is cleared from the DOM.)
The current media query is no longer something components can access; it is determined only by the props of the <Media> component they find themselves in.

That last point presents an interesting problem. How might we represent a component that gets styled differently at different breakpoints? (Let’s imagine a matchMedia example.)

<Sans size={sm ? 2 : 3}>

<>
  <Media at="sm">
    {this.getComponent('sm')}
  </Media>
  <Media greaterThan="sm">
    {this.getComponent()}
  </Media>
</>

getComponent(breakpoint?: string) {
  const sm = breakpoint === 'sm'
  return <Sans size={sm ? 2 : 3} />
}

We're still figuring out patterns for this, so please let us know if you have suggestions.

Development

This project uses auto-release to automatically release on every PR. Every PR should have a label that matches one of the following

Version: Trivial
Version: Patch
Version: Minor
Version: Major

Major, minor, and patch will cause a new release to be generated. Use major for breaking changes, minor for new non-breaking features, and patch for bug fixes. Trivial will not cause a release and should be used when updating documentation or non-project code.

If you don't want to release on a particular PR but the changes aren't trivial then use the Skip Release tag along side the appropriate version tag.

Emiliano-Bucci/fresnel

@artsy/fresnel

Installation

Overview

Basic Example

Server-side Rendering (SSR) Usage

SSR Example

Usage with Gatsby or Next

Example Apps

Why not conditionally render?

API

createMedia

MediaContextProvider

Media

createMediaStyle

onlyMatch

disableDynamicMediaQueries

at

lessThan

greaterThan

greaterThanOrEqual

between

Pros vs Cons

Development