Styled Components Modifiers

Styled Components are incredibly useful when building an application, but the community lacks guidelines and best practices for how to structure, organize, and modify a component library. Fortunately, the CSS ecosystem has several solutions for this, including the very well-thought-out Block, Element, Modifier (BEM) conventions.

This library enhances styled-components by allowing you to use BEM-flavored conventions when building your components.

Styled Components Modifiers

Overview

Blocks and Elements

Our method for structuring Blocks and Elements doesn’t actually require any special tooling. It’s just a simple convention we use for namespacing the components, add the Elements as properties of a Block component:

  // Define your Button styled component (the Block)
  const Button = styled.button``;

  // Define your Icon styled component (the Element)
  const Icon = styled(IconComponent)``;

  // Add the Icon as a property of the Button
  Button.Icon = Icon;

  // To render these components...
  render() {
    return (
      <Button>
        <Button.Icon />
      </Button>
    )
  }

This gives us a nice namespacing that's easy to visualize in a Blocks and Elements structure.

But what about modifiers?

Modifiers

This tool allows you to implement modifiers and apply them to styled-components like this:

<Button modifiers={['success', 'large']}>...</Button>

or as a single string like this:

<Button modifiers="success">...</Button>

The modifiers are passed in as an array of flags or a single flag. Each flag changes the appearance of the Block or Element component. When passing in an array, the values are filtered and only strings are used, which means that it is safe to do the following:

<Button modifiers={['large', isLoading && 'loading']}>...</Button>

which, if isLoading is false, resolves to:

<Button modifiers={['large', false]}>...</Button>

In this case only large will be used.

Installation

This package is available on npm as styled-components-modifiers.

To install the latest stable version with npm:

$ npm install styled-components-modifiers --save

...or with yarn:

$ yarn add styled-components-modifiers

Using Styled Components Modifiers

Defining Modifiers

The core of styled-components-modifiers is a modifier configuration object. The keys in this object become the available flags that can be passed to the component's modifiers prop. Each value defines a function that returns a CSS style string.

For our demo, let's first set up a modifier configuration object:

const MODIFIER_CONFIG = {
  // The functions receive the props of the component as the only argument.
  // Here, we destructure the theme from the argument for use within the modifier styling.
  disabled: ({ theme }) => `
    // These styles are applied any time this modifier is used.
    background-color: ${theme.colors.chrome_400};
    color: ${theme.colors.chrome_100};
  `,

  // Alternatively, you can return an object with your styles under the key `styles`.
  success: ({ theme }) => ({
    styles: `
      background-color: ${theme.colors.success};
    `,
  }),

  // Styled Components exports a `css` util that enables some nice linting and interpolation
  // features. You can use it directly or with the `styles` object pattern.
  warning: ({ theme }) => css`
    background-color: ${theme.colors.warning};
  `,

  large: () => `
    height: 3em;
    width: 6em;
  `,
};

Then, we need to apply the modifier configuration object (MODIFIER_CONFIG) to the styled component we want to modify:

import styled from 'styled-components';
import { applyStyleModifiers } from 'styled-components-modifiers';

const Button = styled.button`
  // Any styles that won't change or may be overruled can go above where you
  // apply the style modifiers. In BEM, these would be the styles you apply in
  // either the Block or Element class's primary definition.
  font-size: 24px;
  padding: 16px;

  // Then apply the modifier configuration.
  ${applyStyleModifiers(MODIFIER_CONFIG)};

  // You can apply as many modifier configurations as you like, but remember that
  // the last modifiers applied take priority in the event of colliding styles.
`;

export default Button;

The end result is a block (Button) with four available modifiers (disabled, success, warning, and large).

Validating Modifiers

Because the modifiers are an arbitrary array of flags, it is very easy to pass a value as a modifier that is not found in the component's modifier configuration object. Fortunately, we have a tool to help with that: you can validate the modifiers prop with styleModifierPropTypes:

// In the Button component's file
import { styleModifierPropTypes } from 'styled-components-modifiers';

// ...the Button definition, as seen above, goes here...

Button.propTypes = {
  modifiers: styleModifierPropTypes(MODIFIER_CONFIG),
};

This will validate that only keys found within our MODIFIER_CONFIG are supplied to the styled component. It will also throw a PropTypes error if an invalid modifier is used.

Applying Modifiers

Applying modifiers when rendering the component is as simple as providing a modifiers prop. The value of this prop can be either a string or an array of strings. Each string value should correspond to keys in the modifier configuration object applied to the component.

function Form() {
  return (
    <div>
      {/* ...the rest of form goes here... */}
      {/* Render a button, and give it a `modifiers` prop with the desired modifier. */}
      <Button modifiers="success" />

      {/* This is also perfectly valid, and will result in "stacked" modifiers. */}
      <Button modifiers={['success', 'large']} />
    </div>
  );
}

You can also apply the modifiers to be responsive. For this, the value of the modifiers prop should be an object where each value is either a string or array of strings that match a modifier name. Which set of modifiers is chosen will be based on the value of a size prop that you must also provide to the component.

<Button
  modifiers={{
    small: 'disabled', // <-- will be applied when `getTheSizeFromSomewhere()` returns 'small'
    medium: ['success', 'large'],
  }}
  size={getTheSizeFromSomewhere()}
/>

Note:

If you apply modifiers using the responsive technique and the value of size doesn't match a key in the object, the value of _ will be applied by default. This is useful for applying special modifiers only on a single size.

<Button
  modifiers={{
    _: 'disabled', // <-- will be applied for all size values _except_ 'medium'.
    medium: ['success', 'large'], // <-- will only be applied if the value of `size` is 'medium'.
  }}
  size={getTheSizeFromSomewhere()}
/>

Responsive Modifiers (deprecated)

This approach to responsive modifiers is deprecated and will be removed in the 2.0 release. The same functionality has been added to the normal modifiers utilities.

When designing components that are intended to be responsive, you may find it useful to apply different styles based on a size prop as shown below.

import styled from 'styled-components';
import {
  applyResponsiveStyleModifiers,
  applyStyleModifiers,
  responsiveStyleModifierPropTypes,
  styleModifierPropTypes,
} from 'styled-components-modifiers';

// Define the MODIFIER_CONFIG in exactly the same way as above. You would use the same
// modifier configuration for responsive and non-responsive modifiers.

const Button = styled.button`
  // ...define your base styles here...

  // Apply the modifier configuration:
  ${applyStyleModifiers(MODIFIER_CONFIG)}

  // Then apply the responsive modifiers.
  // This must happen AFTER the normal modifiers have been applied.
  ${applyResponsiveStyleModifiers(MODIFIER_CONFIG)}
`;

Button.propTypes = {
  // Setup validation of the "normal" modifier flags:
  modifiers: styleModifierPropTypes(MODIFIER_CONFIG),

  // You can also validate the responsive modifier flags:
  responsiveModifiers: responsiveStyleModifierPropTypes(MODIFIER_CONFIG),
};

export default Button;

Using responsive modifiers is a little bit different, though, but just as simple:

<Button
  responsiveModifiers={{
    small: 'disabled',
    medium: ['success', 'large'],
  }}
  size={getTheSizeFromSomewhere()}
/>

It works by matching the size prop provided to the component with the keys of the responsiveModifiers prop, and then applying the appropriate modifier(s) based on the corresponding value in responsiveModifiers.

So, for example, when Button receives a prop size with a value equal to medium, the modifiers success and large will be applied to the Button. If size does not match any key in the responsiveModifiers, no additional modifiers will be applied. Your normal modifiers array will still work exactly the same.

Tada! Responsive styling!

Alternative Prop Names

Finally, let’s say you want to apply multiple modifier arrays, or perhaps you just really don't like naming the prop modifiers. You can name the prop something else when you apply the props to your component:

const Button = styled.button`
  // the prop used for passing modifiers to this button will be
  // named `altPropName` instead of the default `modifiers`:
  ${applyStyleModifiers(MODIFIER_CONFIG, 'altPropName')}
`;

The same can be done when you applyResponsiveStyleModifiers (deprecated).

Built with Styled Components Modifiers

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Contributing

We are thankful for any contributions made by the community. By contributing you agree to abide by the Code of Conduct in our Contributing Guidelines.

License

MIT

Decisiv/styled-components-modifiers

Decisiv

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