styled-token

A small helper function (similar to lodash's _.get function) for accessing tokens from a styled-components theme object.

import token from 'styled-token';

const Link = styled.a`
    color: ${token('colors.blue')};
`;

Why?

Writing styles in styled-components can quickly get very verbose when accessing theme values. Here is one of styled-components theme examples:

const Button = styled.button`
    color: ${props => props.theme.fg};
    border: 2px solid ${props => props.theme.fg};
    background: ${props => props.theme.bg};

    font-size: 1em;
    margin: 1em;
    padding: 0.25em 1em;
    border-radius: 3px;
`;

There is a lot of boilerplate code to first access the props, then access the theme, then finally the colors. With a little bit of cleverness, you can reduce some of the boilerplate:

const Button = styled.button(({ theme }) => css`
    color: ${theme.fg};
    border: 2px solid ${theme.fg};
    background: ${theme.bg};

    font-size: 1em;
    margin: 1em;
    padding: 0.25em 1em;
    border-radius: 3px;
`);

This is a little more manageable, but there is still some boilerplate to make the theme accessible, and the theme structure is very simple. With a larger theme that has nested objects and potentially even namespacing, it can quickly get out of hand:

const Button = styled.button(({ theme }) => css`
    color: ${theme.bootstrap.button.foregroundColor};
    border: 2px solid ${theme.bootstrap.button.foregroundColor};
    background: ${theme.bootstrap.button.backgroundColor};

    font-size: ${theme.bootstrap.fonts.defaultFontSize};
    margin: ${theme.bootstrap.space.lg};
    padding: ${theme.bootstrap.space.xs} ${theme.bootstrap.space.lg};
    border-radius: ${theme.bootstrap.radii.default};
`);

Using the styled-token helper function cleans things up nicely:

import t from 'styled-token';

const Button = styled.button`
    color: ${t('button.foregroundColor')};
    border: 2px solid ${t('button.foregroundColor')};
    background: ${t('button.backgroundColor')};

    font-size: ${t('fonts.defaultFontSize')};
    margin: ${t('space.lg')};
    padding: ${t('space.xs')} ${t('space.lg')};
    border-radius: ${t('radii.default')};
`);

How it works?

Our helper function returns an Interpolation which is passed to the styled-components TaggedTemplateLiteral. An Interpolation is defined as follows:

This can either be a string or a function. Strings are combined with the rules as-is. Functions will receive the styled component's props as the first and only argument.

In our case, the Interpolation is a function that uses the received props to to access the tokens from the theme. You can read more about the magic behind styled-components to get a better understanding of how tagged templates and interpolations work.

Since we are returning an interpolation and not a value, there are a few caveats to keep in mind when using this helper.

API

token( path [, options ] [, callback ] ) => Interpolation

Arguments

1. path (string|array|object): A string path to the token value, an array of paths, or an object of keyed paths. See below for string, array, and object syntax examples.

2. options (object): Options for the token helper.

   • options.namespace (string): The namespace to pull the value from. This will override any namespace defined on the theme.
   • options.defaultValue (any): A fallback value that will be used if the path is not defined.
   • options.caching (bool): Enable caching of results. Do not use this if you mutate the theme directly.

3. callback (function): A callback that will be called with the token value(s).

Returns

Interpolation: A styled-components TaggedTemplateLiteral interpolation.

Examples: String Syntax

// Access nested object properties with ".", or arrays with "[]"
const Link = styled.a`
    font-weight: ${token('fontWeights.bold')};
    color: ${token('colors.blues[3]')};
`;

// Modify the token value after it is retrieved
const Button = styled.button`
    padding: ${token('space.lg', t => t * 2)}px;
`;

// Pull the token from the "light" namespace
const Link = styled.a`
    color: ${token('colors.blue', { namespace: 'light' })};
`;

// Fallback to "#007bff" if the "colors.blue" token is not defined
const Link = styled.a`
    color: ${token('colors.blue', { defaultValue: '#007bff' })};
`;

// Pull the "space.lg" token from the "condensed" namespace, using "24" if it is not defined,
// and then multiplying the result by two
const Button = styled.button`
    padding: ${token('space.lg', { namespace: 'condensed', defaultValue: 24 }, t => t * 2)}px;
`;

Examples: Array Syntax

// Use "colors.brand" if it is defined, otherwise use "colors.blue"
const Link = styled.a`
    color: ${token(['colors.brand', 'colors.blue'])};
`;

// Pull multiple values from the theme using an array
const Button = styled.button`
    padding: ${token(['space.lg', 'space.suffix'], (val, values) => `${values[0] * 2}${values[1]}`)};
`;

Examples: Object Syntax

// Pull multiple values from the theme using an object (with fallback border colors)
const Button = styled.button`
    border: ${token({
        borderColor: ['colors.brand', 'colors.blue'],
        borderWidth: 'button.borderWidth',
        borderStyle: 'button.borderStyle'
    }, ({ borderColor, borderWidth, borderStyle }) => `${borderWidth} ${borderStyle} ${borderColor}`)};
`;

Namespacing

The function supports namespacing via the NAMESPACE property on the theme, or options.namespace on the function.

const theme = {
    NAMESPACE: 'light',
    fontColor: 'darkgray',
    light: {
        fontColor: 'black'
    },
    dark: {
        fontColor: 'white'
    }
};

token('fontColor') // "black"
token('fontColor', { namespace: 'dark' }) // "white"
token('fontColor', { namespace: '' }) // "darkgray"

Global Options

API options can be specified globally by adding a STYLED_TOKEN object on the theme. The most common use for this is to globally enable the caching option. You might also find it useful to set defaultValue globally (by default it will fall back to undefined).

const theme = {
    STYLED_TOKEN: {
        caching: true,
        defaultValue: '',
    }
};

Caveats

Since our helper returns an Interpolation and not a value, there are some situations that you can't use the helper like you would a traditional getter function.

  // Accessing array properties
  const styles = css`
-     color: ${token('colors.blues')[0]};
+     color: ${token('colors.blues[0]')};
  `;

  // Modifying the token value
  const styles = css`
-     font-family: ${token('fonts.sansSerif').replace('Tahoma', 'Geneva')};
+     font-family: ${token('fonts.sansSerif', t => t.replace('Tahoma', 'Geneva'))};
  `;

  // Fallback values
  const styles = css`
-     color: ${token('colors.lightBlue') || token('colors.blue') || '#007bff'};
+     color: ${token(['colors.lightBlue', 'colors.blue'], { defaultValue: '#007bff' })};
  `;