Design Tokens Library

The Design Tokens Library provides two main APIs to work with design tokens:

• The TokensLibrary API articulates design tokens from many sources (e.g: light/dark color values) in collections. Then, it offers a code generation feature to convert design tokens in various languages and flavours (CSS, SCSS, JSON...).
• The TokenTree API provides helps you parse and manipulate a single token tree with rich validation errors, query methods and a mapping API to work the value.

[!NOTE] The Design Tokens Library is compliant with the W3C Design Tokens Specification.

Installation

Using npm

$ npm install @nclsndr/design-tokens-library

Using yarn

$ yarn add @nclsndr/design-tokens-library

Using pnpm

$ pnpm add @nclsndr/design-tokens-library

Usage

Generate code from many token files using the tokensLibrary

Starting point

Let's assume we have a few design tokens files like so:

• A light-colors.json file

{
  "Color": {
    "$type": "color",
    "Accent": {
      "500": {
        "$value": "#1D93DC"
      }
    }
  }
}

• A dark-colors.json file

{
  "Color": {
    "$type": "color",
    "Accent": {
      "500": {
        "$value": "#52B5F3"
      }
    }
  }
}

• A semantic-colors.json file

{
  "Semantic": {
    "$type": "color",
    "Foreground": {
      "$value": "{Color.Accent.500}"
    }
  }
}

Create a library

We'll create a TokensLibrary instance by providing the JSON token trees from the files.

import * as fs from 'node:fs';
import { createTokensLibrary } from '@nclsndr/design-tokens-library';

const lightColorsTree = fs.readFileSync('./light-colors.json', 'utf8');
const darkColorsTree = fs.readFileSync('./dark-colors.json', 'utf8');
const semanticColorsTree = fs.readFileSync('./semantic-colors.json', 'utf8');

const library = createTokensLibrary({
  tokenTrees: [
    // We register the JSON token trees we want to work with
    { name: 'light', jsonTree: lightColorsTree },
    // jsonTree can be either a string or an object (parsed JSON)
    { name: 'dark', jsonTree: darkColorsTree },
    { name: 'semantic', jsonTree: semanticColorsTree },
  ],
  collections: [
    {
      name: 'Color scheme',
      // We declare the modes of the collection
      modes: [
        {
          name: 'light',
          // We associate the token trees to the mode
          tokenTrees: [{ name: 'light' }],
        },
        {
          name: 'dark',
          tokenTrees: [{ name: 'dark' }],
        },
      ],
    },
  ],
});

[!IMPORTANT] When declaring modes within a collection, the token trees must define the same tokens for each mode. Otherwise, the library will throw an error. This ensures that an alias referring to a token with modes, will always resolve to an actual value.

Generate CSS variables

Let's generate two CSS variables files from the Color scheme collection and the Semantic token trees: themed-colors.css and semantic-colors.css. To help us out, we'll use the toCSSVariables exporter.

import { exporter } from '@nclsndr/design-tokens-library';

const cssFiles = library.export(
  exporter.toCSSVariables({
    // We can pass format options to customize the output
    format: { token: { name: { toCase: 'kebabCase' } } },
    files: [
      {
        // Declare a file
        name: 'themed-colors.css',
        content: [
          {
            // Declare a scope for the CSS variables
            scope: ':root',
            with: [
              // Pick the tokens from the Color scheme collection
              { type: 'collection', name: 'Color scheme', mode: 'light' },
            ],
          },
          {
            scope: ':root[data-theme="dark"]',
            with: [{ type: 'collection', name: 'Color scheme', mode: 'dark' }],
          },
        ],
      },
      {
        name: 'semantic.css',
        content: [
          {
            scope: ':root',
            with: [
              // Pick the tokens from the Semantic token tree
              { type: 'tokenTree', name: 'semantic' },
            ],
          },
        ],
      },
    ],
  })
);

for (const file of cssFiles) {
  fs.writeFileSync(file.path, file.content, { encoding: 'utf-8' });
}

🎉

Here you are with two CSS files:

themed-colors.css

:root {
  --color-accent-500: #1d93dc;
}
:root[data-theme='dark'] {
  --color-accent-500: #52b5f3;
}

semantic-colors.css

:root {
  --semantic-foreground: var(--color-accent-500);
}

Inspect a tokens file using the token tree API

We start from a JSON parsed JavaScript object that represents a design token tree.

import { parseJSONTokenTree } from '@nclsndr/design-tokens-library';

const tokens = {
  color: {
    $type: 'color',
    blue: {
      100: {
        $value: '#0d3181',
      },
    },
  },
};

const tokenTree = parseJSONTokenTree(tokens);

The TokenTree exposes various methods to either get the parse errors, the tokens, or work with the values of the tokens.

// Get errors
tokenTree.getErrors();

// Get a given token
tokenTree.getToken(['color', 'blue', 100]);
// with a type guard to help out the TS compiler
tokenTree.getTokenOfType('color', ['color', 'blue', 100]);

// Get tokens
tokenTree.getAllTokens();
tokenTree.getAllTokensByType('color');
// With a callback style
tokenTree.mapTokensByType('color', (token) => {
  // ...
});

// Get groups
tokenTree.getAllGroups();
tokenTree.getGroup(['color']);

Once we grabbed some tokens, we can use the Token methods to move further.

The most basic operation is to get the JSON value of a token. Let's take the following:

const tokens: JSONTokenTree = {
  color: {
    $type: 'color',
    blue: {
      $value: '#0000FF',
    },
    accent: {
      $value: '{color.blue}',
    },
    borderActive: {
      $value: '{color.accent}',
    },
  },
  border: {
    $type: 'border',
    active: {
      $value: {
        width: '1px',
        style: 'solid',
        color: '{color.borderActive}',
      },
    },
  },
};
const tokenTree = parseJSONTokenTree(tokens);

const fullyResolvedColorValues = tokenTree.mapTokensByType('color', (token) => {
  console.log(token.summary);

  return token.getJSONValue({
    resolveAtDepth: Infinity,
    // resolveAtDepth allows to resolve the token value to a certain depth.
  });
});
console.log(fullyResolvedColorValues); // [ '#0000FF', '#0000FF', '#0000FF' ]

const partiallyResolvedColorValues = tokenTree.mapTokensByType(
  'color',
  (token) => {
    return token.getJSONValue({
      resolveAtDepth: 1, // resolving aliases up to 1 level
    });
  }
);
console.log(partiallyResolvedColorValues); // [ '#0000FF', '#0000FF', '{color.blue}' ]

Whenever we want to work with the value of a token, we need to consider all the potential forms the value might take. The token .getValueMapper() method provides an API to generalize the approach to the token values where most of them can be aliased at any point in the tree.

With a color, we might have a raw value or an alias reference.

const colorValues = tokenTree.mapTokensByType('color', (colorToken) => {
  return colorToken
    .getValueMapper()
    .mapScalarValue((scalarValue) => scalarValue.raw)
    .mapAliasReference(
      (aliasReference) => `var(--${aliasReference.to.treePath.array.join('-')})`
    )
    .unwrap();
});
console.log(colorValues); // [ '#0000FF', 'var(--color-blue)', 'var(--color-accent)' ]

With a border, we might have an alias reference or an object, which might contain an alias reference for each of its properties.

const borderValues = tokenTree.mapTokensByType('border', (token) => {
  return token
    .getValueMapper()
    .mapAliasReference((ref) => `var(--${ref.to.treePath.join('-')})`)
    .mapObjectValue((obj) =>
      obj.flatMap((value) => {
        const width = value.width
          .mapAliasReference((ref) => `var(--${ref.to.treePath.join('-')}`)
          .mapScalarValue((value) => value.raw)
          .unwrap();
        const style = value.style
          .mapAliasReference((ref) => `var(--${ref.to.treePath.join('-')}`)
          .mapScalarValue((value) => value.raw)
          .unwrap();
        const color = value.color
          .mapAliasReference((ref) => `var(--${ref.to.treePath.join('-')}`)
          .mapScalarValue((value) => value.raw)
          .unwrap();

        return [width, style, color].join(' ');
      })
    )
    .unwrap();
});

console.log(borderValues); // [ '1px solid var(--color-borderActive' ]

In order to cut down the complexity of aliases one would have to resolve, the token .getValueMapper() methods takes a resolveAtDepth option, which can bring back the raw value of the token at a certain depth, as far as the referenced token exists.

const cssColorTokens = tokenTree.mapTokensByType('color', (colorToken) => {
  return {
    key: colorToken.name,
    value: colorToken
      .getValueMapper({
        resolveAtDepth: Infinity,
      })
      .mapScalarValue((scalarValue) => scalarValue.raw)
      .mapAliasReference(
        (aliasReference) =>
          `var(--${aliasReference.to.treePath.array.join('-')})`
      )
      .unwrap(),
  };
});

API

createTokensLibrary

Create a TokensLibrary instance from many token trees and collections.

type SourceCollection = {
  name: string;
  modes: Array<{
    name: string;
    tokenTrees: Array<{
      name: string;
      tokenTypes?: Array<TokenTypeName>;
      where?: Array<Array<string>>; // [['color','*'], ['dimension','*']]  
    }>;
  }>;
};
type SourceTokenTree = {
  name: string;
  jsonTree: string | Json.Object;
};
declare function createTokensLibrary({ tokenTrees, collections, }: {
  tokenTrees: Array<SourceTokenTree>;
  collections?: Array<SourceCollection>;
}): TokensLibrary;

• TokensLibrary

Exporter

The Exporter API is accessible upon the tokensLibrary.export(/*...*/) method.

type ExporterOutput = Array<{
  type: 'file';
  path: string;
  content: string;
}>

interface TokensLibrary {
  export: <ExporterOptions>(opt: ExporterOptions) => ExporterOutput
}

toCSSVariables

Generate CSS variables from a tokens library.

type ToCSSVariablesOptions = {
  files: Array<{
    name: string;
    content: Array<{
      scope: string;
      with: Array<SelectInLibrary & {
        format?: FormatOptions;
      }>;
    }>;
    format?: FormatOptions;
  }>;
  format?: FormatOptions;
};

type SelectInLibrary = | {
  type: 'tokenTree';
  name: string;
  tokenTypes?: Array<TokenTypeName>;
  where?: Array<Array<string>>; // [['color','*'], ['dimension','*']]  
}
        | {
  type: 'collection';
  name: string;
  mode: string;
  tokenTypes?: Array<TokenTypeName>;
  where?: Array<Array<string>>; // [['color','*'], ['dimension','*']]  
};

type FormatOptions = {
  token?: {
    name?: {
      toCase?: Case;
      joinWith?: string;
      template?: string;
    };
    value?: {
      resolveAtDepth?: number | 'infinity';
    };
  };
};

declare function toCSSVariables(opt: ToCSSVariablesOptions): ExporterOutput;

parseJSONTokenTree

Parse a JSON token tree into a TokenTree instance.

export declare function parseJSONTokenTree(
  jsonTokenTree: unknown, // The JSON token tree to parse, must be string or object. 
  options?: {
    name?: string; // The name of the token tree.
    throwOnError?: boolean; // Whether to throw an error if the JSON token tree is invalid.
}): TokenTree;

• TokenTree
  • Token
    • ValueMapper
      • ScalarValue
      • AliasReference
      • ObjectValue
      • ArrayValue