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React CSS Props

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Dynamically turn your props into CSS clases!


$ yarn add react-css-props

Note: any feedback, contributions or other possible use cases are highly appreciated.


Imagine that you are working in just a regular React project, and you decide to use CSS Modules for your styling. At some point, you would like to have the following components:

<Block width1of4>
    <Button>Generate report</Button>
    <Button disabled>
        <Icon save />Save search

OK. Everything looks normal with the Button component but, wait, what the hell is that custom property besides Block and Icon!? You guessed, those are custom properties already built-in with each component, they match a specific class in the CSS for that component, in a way that you don't have to contemplate every possible prop that will eventually get rendered into a hashed, CSS Modules class. But first, let's get into each component one at a time.

Block component

Say you are implementing your own grid system, something like what Bootstrap does with their col-md-6 col-xs-12 global classes, but you want a wrapper component to do that and, of course, you don't want to rely on classNames to do all the job.

.block {
  padding: $padding-layout-block;
  box-sizing: border-box;
  float: left;
  width: 100%;

@mixin blockSize($n) {
  width: $column-width * $n * 1%;
  .block & {
    padding-top: 0;

@media (#{$breakpoint-phablet-up}) {
  .width1of12 {
    @include blockSize(1);
  .width2of12, .width1of6 {
    @include blockSize(2);
  .width3of12, .width1of4 {
    @include blockSize(3);
  .width4of12, .width2of6, .width1of3 {
    @include blockSize(4);

As you might have noticed, this code us using SASS to show an use case with a preprocessor, but you don't need one at all as long as you are using CSS Modules. This is where react-css-props takes action:

import React from 'react';
import cn from 'classnames';
import cssProps from 'react-css-props';

import theme from './Block.scss';

// First customize it with your theme, then use it!
const toCSS = cssProps(theme);

const Block = ({ children, ...props }) => (
    <div className={cn(theme.block, ...toCSS(props))}>

export default Block;

Obviously, the magic is that cssProps is a HOF (Higher Order Function), that gets ready to use the props ass CSS clases using the imported theme from CSS Modules. As you can imagine, the code before react-css-props was as weird as <Block className="block block-width-1-of-4">.

Icon component

Now let's move into a more complex example. We have the following CSS and we don't have control over it cause it's auto-generated (maybe, by our Designer):

@font-face {
  font-family: Custom Icons;
  src: url("./Icon.woff");

.icon {
  font-family: Custom Icons, Helvetica, sans-serif;
  font-style: normal !important;

.icon-arrow-down:before {
  content: "\e900";

.icon-arrow-left:before {
  content: "\e901";

.icon-arrow-right:before {
  content: "\e902";

.icon-arrow-up:before {
  content: "\e903";

Of course, you really want to avoid as much className duplication as possible, and you notice the pattern of every icon: icon-${type}. Well, luckily, you have a second optional parameter to the react-css-props module to specify a lambda with your given pattern, as follows:

import React from 'react';
import cn from 'classnames';
import cssProps from 'react-css-props';

import theme from './Icon.css';

// Prepare it with your custom mapper function
const toCSS = cssProps(theme, type => `icon-${type}`);

const Icon = (props) => (
    <i className={cn(theme.icon, ...toCSS(props))} />

export default Icon;

Isn't that neat? No longer need for code like this: <Icon className="icon icon-save" />, where you had to type three times the word "icon" to finnally render it!


cssProps(theme: Object, mapper?: (string) => string)

The first argument is the theme imported from CSS Modules which, as confirmed by Mark Dalgleish (the creator of CSS Modules), it's "just a regular JavaScript object :)". The second argument is optional and corresponds to a mapper function in case your CSS clases follow a defined pattern. This method returns the next function (you can name any of these two literally whatever you like):

toCSS(props: Object, defaultClass?: string): Array<string>

The first argument are the props of your component, likely to have been delegated to only your plausible CSS classes with the spread operator (...props). The second argument is also optional and consists on a default CSS class, if you have any. This method will always return a string array of matching CSS classes between your theme and your props. This plays along very well with classnames to customize your components, as shown in the examples.


  • Flow - a static type checker for JavaScript.
  • Jest - painless JavaScript testing.
  • Yarn - fast, reliable, and secure dependency management.


MIT © Flavio Corpa

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