Aphrodite: Inline Styles that work

Support for colocating your styles with your JavaScript component.

• Works great with and without React
• Supports media queries without window.matchMedia
• Supports pseudo-selectors like :hover, :active, etc. without needing to store hover or active state in components. :visited works just fine too.
• Supports automatic global @font-face detection and insertion.
• Respects precedence order when specifying multiple styles
• Requires no AST transform
• Injects only the exact styles needed for the render into the DOM.
• Can be used for server rendering
• Few dependencies, small (20k, 6k gzipped)
• No external CSS file generated for inclusion
• Autoprefixes styles

Installation

Aphrodite is distributed via npm:

npm install --save aphrodite

API

If you'd rather watch introductory videos, you can find them here.

import React, { Component } from 'react';
import { StyleSheet, css } from 'aphrodite';

class App extends Component {
    render() {
        return <div>
            <span className={css(styles.red)}>
                This is red.
            </span>
            <span className={css(styles.hover)}>
                This turns red on hover.
            </span>
            <span className={css(styles.small)}>
                This turns red when the browser is less than 600px width.
            </span>
            <span className={css(styles.red, styles.blue)}>
                This is blue.
            </span>
            <span className={css(styles.blue, styles.small)}>
                This is blue and turns red when the browser is less than
                600px width.
            </span>
        </div>;
    }
}

const styles = StyleSheet.create({
    red: {
        backgroundColor: 'red'
    },

    blue: {
        backgroundColor: 'blue'
    },

    hover: {
        ':hover': {
            backgroundColor: 'red'
        }
    },

    small: {
        '@media (max-width: 600px)': {
            backgroundColor: 'red',
        }
    }
});

Conditionally Applying Styles

Note: If you want to conditionally use styles, that is simply accomplished via:

const className = css(
  shouldBeRed() ? styles.red : styles.blue,
  shouldBeResponsive() && styles.small,
  shouldBeHoverable() && styles.hover
)

<div className={className}>Hi</div>

This is possible because any falsey arguments will be ignored.

Combining Styles

To combine styles, pass multiple styles or arrays of styles into css(). This is common when combining styles from an owner component:

class App extends Component {
    render() {
        return <Marker styles={[styles.large, styles.red]} />;
    }
}

class Marker extends Component {
    render() {
        // css() accepts styles, arrays of styles (including nested arrays),
        // and falsy values including undefined.
        return <div className={css(styles.marker, this.props.styles)} />;
    }
}

const styles = StyleSheet.create({
    red: {
        backgroundColor: 'red'
    },

    large: {
        height: 20,
        width: 20
    },

    marker: {
        backgroundColor: 'blue'
    }
};

Server-side rendering

To perform server-side rendering, make a call to StyleSheetServer.renderStatic, which takes a callback. Do your rendering inside of the callback and return the generated HTML. All of the calls to css() inside of the callback will be collected and the generated css as well as the generated HTML will be returned.

Rehydrating lets Aphrodite know which styles have already been inserted into the page. If you don't rehydrate, Aphrodite might add duplicate styles to the page.

To perform rehydration, call StyleSheet.rehydrate with the list of generated class names returned to you by StyleSheetServer.renderStatic.

As an example:

import { StyleSheetServer } from 'aphrodite';

// Contains the generated html, as well as the generated css and some
// rehydration data.
var {html, css} = StyleSheetServer.renderStatic(() => {
    return ReactDOMServer.renderToString(<App/>);
});

// Return the base HTML, which contains your rendered HTML as well as a
// simple rehydration script.
return `
    <html>
        <head>
            <style data-aphrodite>${css.content}</style>
        </head>
        <body>
            <div id='root'>${html}</div>
            <script src="./bundle.js"></script>
            <script>
                StyleSheet.rehydrate(${JSON.stringify(css.renderedClassNames)});
                ReactDOM.render(<App/>, document.getElementById('root'));
            </script>
        </body>
    </html>
`;

Disabling !important

By default, Aphrodite will append !important to style definitions. This is intended to make integrating with a pre-existing codebase easier. If you'd like to avoid this behaviour, then instead of importing aphrodite, import aphrodite/no-important. Otherwise, usage is the same:

import { StyleSheet, css } from 'aphrodite/no-important';

Font Faces

Creating custom font faces is a special case. Typically you need to define a global @font-face rule. In the case of Aphrodite we only want to insert that rule if it's actually being referenced by a class that's in the page. We've made it so that the fontFamily property can accept a font-face object (either directly or inside an array). A global @font-face rule is then generated based on the font definition.

const coolFont = {
    fontFamily: "CoolFont",
    fontStyle: "normal",
    fontWeight: "normal",
    src: "url('coolfont.woff2') format('woff2')"
};

const styles = StyleSheet.create({
    headingText: {
        fontFamily: coolFont,
        fontSize: 20
    },
    bodyText: {
        fontFamily: [coolFont, "sans-serif"]
        fontSize: 12
    }
});

Aphrodite will ensure that the global @font-face rule for this font is only inserted once, no matter how many times it's referenced.

Animations

Similar to Font Faces, Aphrodite supports keyframe animations, but it's treated as a special case. Once we find an instance of the animation being referenced, a global @keyframes rule is created and appended to the page.

Animations are provided as objects describing the animation, in typical @keyframes fashion. Using the animationName property, you can supply a single animation object, or an array of animation objects. Other animation properties like animationDuration can be provided as strings.

const translateKeyframes = {
    '0%': {
        transform: 'translateX(0)',
    },

    '50%': {
        transform: 'translateX(100px)',
    },

    '100%': {
        transform: 'translateX(0)',
    },
};

const opacityKeyframes = {
    'from': {
        opacity: 0,
    },

    'to': {
        opacity: 1,
    }
};

const styles = StyleSheet.create({
    zippyHeader: {
        animationName: [translateKeyframes, opacityKeyframes],
        animationDuration: '3s, 1200ms',
        animationIterationCount: 'infinite',
    },
});

Aphrodite will ensure that @keyframes rules are never duplicated, no matter how many times a given rule is referenced.

Use without React

Aphrodite was built with React in mind, but does not depend on React. Here, you can see it used with Web Components:

import { StyleSheet, css } from 'aphrodite';

const styles = StyleSheet.create({
    red: {
        backgroundColor: 'red'
    }
});

class App extends HTMLElement {
    attachedCallback() {
        this.innerHTML = `
            <div class="${css(styles.red)}">
                This is red.
            </div>
        `;
    }
}

document.registerElement('my-app', App);

Caveats

Style injection and buffering

Aphrodite will automatically attempt to create a <style> tag in the document's <head> element to put its generated styles in. Aphrodite will only generate one <style> tag and will add new styles to this over time. If you want to control which style tag Aphrodite uses, create a style tag yourself with the data-aphrodite attribute and Aphrodite will use that instead of creating one for you.

To speed up injection of styles, Aphrodite will automatically try to buffer writes to this <style> tag so that minimum number of DOM modifications happen.

Aphrodite uses asap to schedule buffer flushing. If you measure DOM elements' dimensions in componentDidMount or componentDidUpdate, you can use setTimeout function to ensure all styles are injected.

import { StyleSheet, css } from 'aphrodite';

class Component extends React.Component {
    render() {
        return <div ref="root" className={css(styles.div)} />;
    }

    componentDidMount() {
        // At this point styles might not be injected yet.
        this.refs.root.offsetHeight; // 0 or 10

        setTimeout(() => {
            this.refs.root.offsetHeight; // 10
        }, 0);
    }
}

const styles = StyleSheet.create({
    div: {
        height: 10,
    },
});

Assigning a string to a content property for a pseudo-element

When assigning a string to the content property it requires double or single quotes in CSS. Therefore with Aphrodite you also have to provide the quotes within the value string for content to match how it will be represented in CSS.

As an example:

const styles = StyleSheet.create({
  large: {
      ':after': {
        content: '"Aphrodite"',
      },
    },
  },
  small: {
      ':before': {
        content: "'Aphrodite'",
      },
    },
  });

The generated css will be:

  .large_im3wl1:after {
      content: "Aphrodite" !important;
  }

  .small_ffd5jf:before {
      content: 'Aphrodite' !important;
  }

Overriding styles

When combining multiple aphrodite styles, you are strongly recommended to merge all of your styles into a single call to css(), and should not combine the generated class names that aphrodite outputs (via string concatenation, classnames, etc.). For example, if you have a base style of foo which you are trying to override with bar:

Do this:

const styles = StyleSheet.create({
  foo: {
    color: 'red'
  },

  bar: {
    color: 'blue'
  }
});

// ...

const className = css(styles.foo, styles.bar);

Don't do this:

const styles = StyleSheet.create({
  foo: {
    color: 'red'
  },

  bar: {
    color: 'blue'
  }
});

// ...

const className = css(styles.foo) + " " + css(styles.bar);

Why does it matter? Although the second one will produce a valid class name, it cannot guarantee that the bar styles will override the foo ones. The way the CSS works, it is not the class name that comes last on a element that matters, it is specificity. When we look at the generated CSS though, we find that all of the class names have the same specificity, since they are all a single class name:

.foo_im3wl1 {
  color: red;
}

.bar_hxfs3d {
  color: blue;
}

In the case where the specificity is the same, what matters is the order that the styles appear in the stylesheet. That is, if the generated stylesheet looks like

.foo_im3wl1 {
  color: red;
}
.bar_hxfs3d {
  color: blue;
}

then you will get the appropriate effect of the bar styles overriding the foo ones, but if the stylesheet looks like

.bar_hxfs3d {
  color: blue;
}
.foo_im3wl1 {
  color: red;
}

then we end up with the opposite effect, with foo overriding bar! The way to solve this is to pass both of the styles into aphrodite's css() call. Then, it will produce a single class name, like foo_im3wl1-o_O-bar_hxfs3d, with the correctly overridden styles, thus solving the problem:

.foo_im3wl1-o_O-bar_hxfs3d {
  color: blue;
}

Object key ordering

When styles are specified in Aphrodite, the order that they appear in the actual stylesheet depends on the order that keys are retrieved from the objects. This ordering is determined by the JavaScript engine that is being used to render the styles. Sometimes, the order that the styles appear in the stylesheet matter for the semantics of the CSS. For instance, depending on the engine, the styles generated from

const styles = StyleSheet.create({
    ordered: {
        margin: 0,
        marginLeft: 15,
    },
});
css(styles.ordered);

you might expect the following CSS to be generated:

margin: 0px;
margin-left: 15px;

but depending on the ordering of the keys in the style object, the CSS might appear as

margin-left: 15px;
margin: 0px;

which is semantically different, because the style which appears later will override the style before it.

This might also manifest as a problem when server-side rendering, if the generated styles appear in a different order on the client and on the server.

If you experience this issue where styles don't appear in the generated CSS in the order that they appear in your objects, there are two solutions:

1. Don't use shorthand properties. For instance, in the margin example above, by switching from using a shorthand property and a longhand property in the same styles to using only longhand properties, the issue could be avoided.

   const styles = StyleSheet.create({
       ordered: {
           marginTop: 0,
           marginRight: 0,
           marginBottom: 0,
           marginLeft: 15,
       },
   });

2. Specify the ordering of your styles by specifying them using a Map. Since Maps preserve their insertion order, Aphrodite is able to place your styles in the correct order.

   const styles = StyleSheet.create({
       ordered: new Map([
           ["margin", 0],
           ["marginLeft", 15],
       ]),
   });

   Note that Maps are not fully supported in all browsers. It can be polyfilled by using a package like es6-shim.

Advanced: Extensions

Extra features can be added to Aphrodite using extensions.

To add extensions to Aphrodite, call StyleSheet.extend with the extensions you are adding. The result will be an object containing the usual exports of Aphrodite (css, StyleSheet, etc.) which will have your extensions included. For example:

// my-aphrodite.js
import {StyleSheet} from "aphrodite";

export default StyleSheet.extend([extension1, extension2]);

// styled.js
import {StyleSheet, css} from "my-aphrodite.js";

const styles = StyleSheet.create({
    ...
});

Note: Using extensions may cause Aphrodite's styles to not work properly. Plain Aphrodite, when used properly, ensures that the correct styles will always be applied to elements. Due to CSS specificity rules, extensions might allow you to generate styles that conflict with each other, causing incorrect styles to be shown. See the global extension below to see what could go wrong.

Creating extensions

Currently, there is only one kind of extension available: selector handlers. These kinds of extensions let you look at the selectors that someone specifies and generate new selectors based on them. They are used to handle pseudo-styles and media queries inside of Aphrodite. See the defaultSelectorHandlers docs for information about how to create a selector handler function.

To use your extension, create an object containing a key of the kind of extension that you created, and pass that into StyleSheet.extend():

const mySelectorHandler = ...;

const myExtension = {selectorHandler: mySelectorHandler};

const { StyleSheet: newStyleSheet, css: newCss } = StyleSheet.extend([myExtension]);

As an example, you could write an extension which generates global styles like

const globalSelectorHandler = (selector, _, generateSubtreeStyles) => {
    if (selector[0] !== "*") {
        return null;
    }

    return generateSubtreeStyles(selector.slice(1));
};

const globalExtension = {selectorHandler: globalSelectorHandler};

This might cause problems when two places try to generate styles for the same global selector however! For example, after

const styles = StyleSheet.create({
    globals: {
        '*div': {
            color: 'red',
        },
    }
});

const styles2 = StyleSheet.create({
    globals: {
        '*div': {
            color: 'blue',
        },
    },
});

css(styles.globals);
css(styles2.globals);

It isn't determinate whether divs will be red or blue.

Changelog

1.1.0

• Animations now support multiple animations per style (see section on Animations) (PR #167)

1.0.0

• Syntax extensions (see section on Advanced extensions) (PR #95)

0.6.0

• css() will now accept arbitrarily nested arrays. i.e. instead of css(styles.a, styles.b), you can now do css([styles.a, [styles.b, styles.c]]). (PR #154)
• Support for multiple font styles with the same font-family. (PR #82)

Tools

• Aphrodite output tool - Paste what you pass to StyleSheet.create and see the generated CSS

TODO

• Add JSdoc
• Consider removing !important from everything.

Other solutions

• js-next/react-style
• dowjones/react-inline-style
• martinandert/react-inline
• milesj/aesthetic - a React style abstraction layer with theme support

License (MIT)

Copyright (c) 2016 Khan Academy

Includes works from https://github.com/garycourt/murmurhash-js, which is MIT licensed with the following copyright:

Copyright (c) 2011 Gary Court

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.