$ yarn add jss-emotion
#OR
$ npm install --save jss-emotion

Usage

./MyComponent.tsx

import { createUseClassNames } from "./useClassNames";

const { useClassNames } = createUseClassNames<Props & { color: "red" | "blue" }>()({
   (theme, { color })=> ({
       "root": { 
           color,
           "&:hover": {
               "backgroundColor": "lightGrey"
           }
        }
   })
});

function MyComponent(props: Props){

    const [ color, setColor ]= useState<"red" | "blue">("red");

    const { classNames }=useClassNames({...props, color });

    return <span className={classNames.root}>hello world</span>;

}

./useClassNames.ts

import { createUseClassNamesFactory } from "jss-emotion";

const theme = {
    "primaryColor": "blue";
};

function useTheme(){
    return theme;
}

export const { createUseClassNames } = createUseClassNamesFactory({ useTheme });

Why this instead of JSS?

Consider this example use of JSS:

//JSS in bundled in @material-ui
import { makeStyles, createStyles } from "@material-ui/core/styles";

type Props = {
    color: "red" | "blue";
};

const useStyles = makeStyles(
  theme => createStyles<"root" | "label">, Props>({
    "root": {
        "backgroundColor": theme.palette.primary.main
    },
    "label": ({ color })=>({
        color
    })
  })
);

function MyComponent(props: Props){

    const classes = useStyles(props);

    return (
        <div className={classes.root}>
            <span className={classes.label}>
                Hello World
            </span>
        </div>
    );

}

Many pain points:

• Because TypeScript doesn't support partial argument inference, we have to explicitly enumerate the classes name as an union type "root" | "label".
• We shouldn't have to import createStyles to get correct typings.
• Inconsistent naming conventions makeStyles -> useStyles -> classes

Let's now compare with jss-emotion

import { createUseClassNames } from "./useClassNames";

type Props = {
    color: "red" | "blue";
};

const { useClassNames } = createUseClassNames<Props>()(
  (theme, { color })=> ({
    "root": {
        "backgroundColor": theme.palette.primary.main
    },
    "label": { color }
  })
);

function MyComponent(props: Props){

    const { classNames } = useClassNames(props);

    return (
        <div className={classNames.root}>
            <span className={classNames.label}>
                Hello World
            </span>
        </div>
    );

}

Benefits:

• Less verbose, same type safety.
• Consistent naming convention createUseClassNames -> useClassNames -> classNames.
• You don't need to remember how things are supposed to be named, just let intellisense guide you.

Besides, JSS, at least the version bundled into material-ui, have other problems:

• It has one major bug: see issue
• JSS has poor performances compared to emotion source

Why not Styled component ?

See this issue

API Reference

This module exports:

• createUseClassNamesFactory()
• css: Reexport of import { css } from "@emotion/css"
• keyframes:Reexport of import { keyframes } from "@emotion/css"
• cx: Reexport of import { cx } from "@emotion/css"
• injectGlobal: Reexport of import { injectGlobal } from "@emotion/injectGlobal"