If-sf NPM | npm.io

sf (speculative fabulation)

generate themes, theme objects, and theme tokens

merge/extend by default. explicit overrides
opt-in/opt-out of tokens and components
roll out your own tokens and components

quick start
motivations
patterns
current tokens

quick start

yarn add if-sf

Wherever you're defining your theme:

import { ThemeProvider } from 'theme-ui';
import { genTheme } from 'if-sf';

const theme = genTheme();

function MyApp() {
  return (
    <ThemeProvider theme={theme}>
      <App />
    </ThemeProvider>
  )
}

If you need access to more granular primitives, you can import individual generators and components:

import { Button } from 'if-sf/components';
import { defaultButtonStyles, genButton } from 'if-sf/tokens';

motivations

sf is built on top of emotion and styled-system's variants. In the past, I've enjoyed working with both, utilizing variants in my emotion or styled-components mark up. However, I found it difficult to think about how component variants should live on the theme object. Additionally, it became difficult to think about how to extend components that had variations -- what if I needed an additional variant typing? What if I wanted to wholesale override the variants? I had similar difficulties on a smaller scale with theme tokens -- what's the best way to override breakpoints? What if I want to extend certain color properties, while overriding others?

sf answers these questions by thinking in terms of merging, extending, and overriding. Using generator functions that receive and return objects, sf generates theme objects to pass into emotion's theme provider while also allowing granular control over how that theme is generated. Here's an example of generating color tokens:

import { genColors } from '@theme/tokens';

const colors = genColors();
/**
 * returns generic color object
 * 
 * colors = { 
 *  text: '#111827',
 *  background: '#F9FAFB',
 *  primary: '#2563EB',
 *  secondary: '#de7283',
 *  accent: '#7C3AED',
 *  muted: '#88d1ff'
 * }
 * 
 */
const mergeColors = genColors({ primary: 'red' }); // replaces 'primary' key in colors object
const extendColors = genColors({ red: 'red' }); // adds 'red' key to colors object
const overrideColors = genColors({ override: { red: 'red' }}); // replaces color object with override object

We can do similar things with more complicated tokens. Checkout the tests for the button component and breakpoints to see how sf handles overrides and merges.

tl;dr

Put object in, get object out
Merge your object or
Override tokens wholesale

patterns

merge styles // map variants

const componentStyle = {
  ...objectStyles,
  variants: [
    {
      key: props => variant({})
    }
  ]
}

const stylesForEmotion = mergeStyles(defaultStyles, props); // returns objectStyles

Using this shape, we can merge the object styles and reduce the variants into something emotion can consume. Additionally, this allows us to use the props available at the component level to generate particular variants.

const Button = styled.button`
  ${props => mergeStyles(defaultStyles, props)}
`;

Because mergeStyles() just returns a styles object, we can opt-in to variants at the component level. We can also add additional styles beyond what the variant provides.