Theo is a an abstraction for transforming and formatting Design Tokens
JavaScript HTML
aputinski Merge pull request #164 from geraldfullam/topic/163-improve-docs-for-…

Fixes issue #163: Improve documentation for `html` under Formats
Latest commit 279cb5c Jul 16, 2018

Theo logo Theo

Build Status NPM version

Theo is an abstraction for transforming and formatting Design Tokens.

Looking for the gulp plugin?

As of Theo v6, the gulp plugin is distributed as a separate package: gulp-theo.


# buttons.yml
    value: "{!primary_color}"
  - ./aliases.yml
  type: color
  category: buttons
# aliases.yml
    value: "#0070d2"
const theo = require('theo');

    transform: {
      type: 'web',
      file: 'buttons.yml'
    format: {
      type: 'scss'
  .then(scss => {
    // $button-background: rgb(0, 112, 210);
  .catch(error => console.log(`Something went wrong: ${error}`));


Theo is divided into two primary features: transforms and formats.

Transforms are a named group of value transforms. Theo ships with several predefined transforms.

Name Value Transforms
raw []
web ['color/rgb']
ios ['color/rgb', 'relative/pixelValue', 'percentage/float']
android ['color/hex8argb', 'relative/pixelValue', 'percentage/float']

Value Transforms

Value transforms are used to conditionaly transform the value of a property. Below are the value transforms that ship with Theo along with the predicate that triggers them.

Name Predicate Description
color/rgb prop.type === 'color' Convert to rgb
color/hex prop.type === 'color' Convert to hex
color/hex8rgba prop.type === 'color' Convert to hex8rgba
color/hex8argb prop.type === 'color' Convert to hex8argb
percentage/float /%/.test(prop.value) Convert a percentage to a decimal percentage
relative/pixel isRelativeSpacing Convert a r/em value to a pixel value
relative/pixelValue isRelativeSpacing Convert a r/em value to a pixel value (excluding the px suffix)

Custom Transforms / Value Transforms

    type: 'easing',
    value: [1,2,3,4]

  // Name to be used with registerTransform()
  // Determine if the value transform
  // should be run on the specified prop
  prop => prop.get("type") === "easing",
  // Return the new value
  prop => {
    const [x1, y1, x2, y2] = prop.get("value").toArray();
    return `cubic-bezier(${x1}, ${y1}, ${x2}, ${y2})`;

// Override the default "web" transform
theo.registerTransform("web", ["color/rgb", "easing/web"]);


Theo ships with the following predefined formats.


:root {
  /* If prop has 'comment' key, that value will go here. */
  --prop-name: PROP_VALUE;


/* If prop has 'comment' key, that value will go here. */
@value prop-name: PROP_VALUE;


// If prop has 'comment' key, that value will go here.
$prop-name: PROP_VALUE;


// If prop has 'comment' key, that value will go here.
$prop-name: PROP_VALUE


// If prop has 'comment' key, that value will go here.
@prop-name: PROP_VALUE;


// If prop has 'comment' key, that value will go here.
$prop-name = PROP_VALUE


$file-name-map: (
  // If prop has 'comment' key, that value will go here.
  "prop-name": (PROP_VALUE),


$file-name-map: (
  // If prop has 'comment' key, that value will go here.
  "prop-name": ($prop-name)


$file-name-list: (
  // If prop has 'comment' key, that value will go here.


// If prop has 'comment' key, that value will go here.
export const propName = 'PROP_VALUE';


module.exports = {
  // If prop has 'comment' key, that value will go here.
  propName: 'PROP_VALUE'


// When passing "format" options to theo.convert(), this format can be
// passed with an additional options object.
let formatOptions = {
  type: 'html',
  options: {
    transformPropName: name => name.toUpperCase()

Configurable options

Option Type Default Description
transformPropName function lodash/camelCase Converts name to camel case.

Supported categories

Tokens are grouped by category then categories are conditionally rendered under a human-friendly display name. Tokens with category values not in this list will still be converted and included in the generated output for all other formats.

Category Friendly Name
spacing Spacing
sizing Sizing
font Fonts
font-style Font Styles
font-weight Font Weights
font-size Font Sizes
line-height Line Heights
font-family Font Families
border-style Border Styles
border-color Border Colors
radius Radius
border-radius Border Radii
hr-color Horizontal Rule Colors
background-color Background Colors
gradient Gradients
background-gradient Background Gradients
drop-shadow Drop Shadows
box-shadow Box Shadows
inner-shadow Inner Drop Shadows
text-color Text Colors
text-shadow Text Shadows
time Time
media-query Media Queries




  "props": {
    "PROP_NAME": {
      "value": "PROP_VALUE",
      "type": "PROP_TYPE",
      "category": "PROP_CATEGORY"


  "properties": [
      "name": "propName",
      "value": "PROP_VALUE",
      "type": "PROP_TYPE",
      "category": "PROP_CATEGORY"


<?xml version="1.0" encoding="utf-8"?>
  <color name="PROP_NAME" category="PROP_CATEGORY">PROP_VALUE</color>
  <dimen name="PROP_NAME" category="PROP_CATEGORY">PROP_VALUE</dimen>
  <string name="PROP_NAME" category="PROP_CATEGORY">PROP_VALUE</string>
  <integer name="PROP_NAME" category="PROP_CATEGORY">PROP_VALUE</integer>
  <property name="PROP_NAME" category="PROP_CATEGORY">PROP_VALUE</property>


  <aura:token name="propName" value="PROP_VALUE" />

Custom Format (Handlebars)

const theo = require('theo');

  // Source: {{stem meta.file}}
  module.exports = [
    {{#each props as |prop|}}
      {{#if prop.comment}}{{{commoncomment prop.comment}}}{{/if}}
      ['{{camelcase}}', '{{prop.value}}'],

A plethora of handlebars helpers, such as camelcase and stem, are available and will assist in formatting strings in templates.

Custom Format (function)

You may also register a format using a function:

const camelCase = require('lodash/camelCase');
const path = require('path');
const theo = require('theo');

theo.registerFormat('array.js', result => {
  // "result" is an Immutable.Map
  return `
    module.exports = [
      // Source: ${path.basename(result.getIn(['meta', 'file']))}
          prop => `
        ['${camelCase(prop.get('name'))}', '${prop.get('value')}'],


type ConvertOptions = {
  transform: TransformOptions,
  format: FormatOptions

type TransformOptions = {
  // If no "type" is specified, values will not be transformed
  type?: string,
  // Path to a token file
  // or just a filename if using the "data" option
  file: string,
  // Pass in a data string instead of reading from a file
  data?: string

type FormatOptions = {
  type: string,
  // Available to the format function/template
  options?: object

type Prop = Immutable.Map
type Result = Immutable.Map

theo.convert(options: ConvertOptions): Promise<string>

theo.convertSync(options: ConvertOptions): string

  name: string,
  // Either a handlebars template string
  // or a function that returns a string
  format: string | (result: Result) => string
): void

  // Referenced in "registerTransform"
  name: string,
  // Indicate if the transform should run for the provided prop
  predicate: (prop: Prop) => boolean,
  // Return the new "value"
  transform: (prop: Prop) => any
): void

  name: string,
  // An array of registered value transforms
  valueTransforms: Array<string>
): void


Please refer to the documentation of the CLI

Design Tokens

Theo consumes Design Token files which are a central location to store design related information such as colors, fonts, widths, animations, etc. These raw values can then be transformed and formatted to meet the needs of any platform.

Let's say you have a web, native iOS, and native Android application that would like to share information such as background colors.

The web might like to consume the colors as hsla values formatted as Sass variables in an .scss file.

iOS might like rgba values formatted as .json.

Finally, Android might like 8 Digit Hex (AARRGGBB) values formatted as .xml.

Instead of hard coding this information in each platform/format, Theo can consume the centralized Design Tokens and output files for each platform.


A Design Token file is written in either JSON (JSON5 supported) or YAML and should conform to the following spec:

  // Required
  // A map of property names and value objects
  "props": {
    "color_brand": {
      // Required
      // Can be any valid JSON value
      "value": "#ff0000",

      // Required
      // Describe the type of value
      // [color|number|...]
      "type": "color",

      // Required
      // Describe the category of this property
      // Often used for style guide generation
      "category": "background",

      // Optional
      // This value will be included during transform
      // but excluded during formatting
      "meta": {
        // This value might be needed for some special transform
        "foo": "bar"
  // Optional
  // Alternatively, you can define props as an array
  // Useful for maintaining source order in output tokens
  "props": [
      // Required
      "name": "color_brand",
      // All other properties same as above

  // Optional
  // This object will be merged into each property
  // Values defined on a property level will take precedence
  "global": {
    "category": "some-category",
    "meta": {
      "foo": "baz"

  // Optional
  // Share values across multiple props
  // Aliases are resolved like: {!sky}
  "aliases": {
    "sky": "blue",
    "grass": {
      "value": "green",
      "yourMetadata": "How grass looks"

  // Optional
  // Array of design token files to be imported
  // "aliases" will be imported as well
  // "aliases" will already be resolved
  // "global" will already be merged into each prop
  // Imports resolve according to the Node.js module resolution algorithm: 
  "imports": [
    // Absolute file path
    // Relative file path: resolves from the directory of the file where the import occurs
    // Module path