Adding Theme UI Components to DefinitelyTyped

Jan 19, 2020 · ☕☕ 7 min read

Epistemic Effort: Low-to-medium effort. It isn't my best work, but I hope it shows that contributing to DefinitelyTyped isn't scary. I might refine it into a meetup talk or a tutorial someday.


I’m using both theme-ui and chakra-ui in an app, and it just doesn’t work. Don’t get me wrong, they’re both really good libraries, and they’re both using @emotion/core to provide the dynamic styling API that IMHO encourages good composition and makes styling faster.

You just shouldn’t use both at once because they step on each other feet. I’d probably go with Chakra, because this is an app, not a blog or a landing page, and I expect I’ll need most of the components from it. However, we’ve decided that theming is a must-have feature of our app.

I’m going to swap Chakra with @theme-ui/components, to get the bundle size lower and satisfy my theming needs. The problem is, this package has no typings. Jxnblk builds great stuff for styling the modern web, but I just can’t use any library without types. It’s not you, it’s me, and I need to do something about it.


git clone --depth 1 --branch master git@github.com:DefinitelyTyped/DefinitelyTyped.git

Well, here we go again. I don’t want to do it. I don’t have time to do it. Yet, it is a noble thing to do, and someone has to.

> npx dts-gen --dt --name @theme-ui/components --template module
npx: installed 59 in 6.878s
Unexpected crash! Please log a bug with the commandline you specified.
ENOENT: no such file or directory, mkdir 'types\@theme-ui\components'

Well, obviously. Since @theme-ui/components is in theme-ui namespace and we can’t have a directory with a slash in name, we need to stick to the conventional workaround.

It doesn't crash anymore in January 2020.
> npx dts-gen --dt --name theme-ui__components --template module -o
npx: installed 59 in 7.202s
Warning: Could not retrieve version/homepage information: HTTP Error 404: Not Found for http://registry.npmjs.org/theme-ui__components

Oh right. It worked, though.

> ls ./types/theme-ui__components
index.d.ts  theme-ui__components-tests.ts  tsconfig.json  tslint.json


Let’s fill in the header comment in index.d.ts

// Type definitions for @theme-ui/components 0.2.50
// Project: https://github.com/system-ui/theme-ui
// Definitions by: Piotr Monwid-Olechnowicz <https://github.com/hasparus>
// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
// TypeScript Version: 3.7


theme-ui reexports a bunch of components from its index.js, let’s list them here.

Box, Flex, Grid, Button, Link, Text, Heading, Image, Card, Label, Input, Select, Textarea, Radio, Checkbox, Slider, Field, Progress, Donut, Spinner, Avatar, Badge, Close, Alert, Divider, Embed, AspectRati, AspectImag, Containe, NavLin, Message, IconButton, MenuButton

Quite a lot of them, right? With a little of multi-cursor karate, I’ve made a stub of the definitions.

export const Box: React.FC;
export const Flex: React.FC;

This isn’t really useful, but I’ll make a commit and push to my fork in case my computer blows up or anything.


I’ve looked a bit in theme-ui repo for issues including TypeScript and found this one. The last comment is a question about @theme-ui/components from yesterday. I’m not the only who needs it. Awesome.

I’ve added a simple test in theme-ui__components-tests.tsx. Just creating all elements with no props. I had to modify paths in tsconfig to get the import working, because there’s a lint rule here prohibiting relative imports.

  "paths": {
      "@theme-ui/components": ["theme-ui__components"]

Let’s start from the Box. This should be the hardest one.


There are some dependencies here.

import styled from "@emotion/styled";
import css, { get } from "@styled-system/css";
import { createShouldForwardProp } from "@styled-system/should-forward-prop";
import space from "@styled-system/space";
import color from "@styled-system/color";

I have a strong feeling that I’ll need types from them. I’ll have to add package.json with the ones that have types outside of DT to my theme-ui__components directory and add them to dependencies whitelist in types publisher, if they’re not there already.

This leaves me with styled-system packages. I’ll add @styled-system/css to paths and I’ll just ignore the props given by space and color for now.

Box gets its props from these 5 functions:

  props => props.css

So sx and css props give us a css prop syntax with no JSX pragma. This gets me to

export interface BoxProps {
  css: Interpolation;
  sx: SxStyleProp;


Gotta take a break now. I’ll continue in the morning. Maybe I’ll even post a half-assed PR so the other guy could continue my work.


I’m starting work at 10. I gotta move fast. variant will be a string, and I’ve just found the names of space props. Not sure what to do with them yet. Should I pick them from AllSystemCSSProperties?

I’m getting any in sx prop properties in tests 😢 Since the dependency on @styled-system/css is aliased and @styled-system/css depends on csstype, I’m gonna go to types/styled-system__css dir and run yarn.

(property) bg?: string | string[] | SystemCssProperties | CSSPseudoSelectorProps | CSSSelectorObject | VariantProperty | UseThemeFunction | (string | ... 2 more ... | undefined)[] | ((theme: any) => ResponsiveStyleValue<...>) | undefined
The background-color CSS property sets the background color of an element.



Okay, I’ve found actual SpaceProps type in @types/styled-system. I’ve already started building this type, copying JSDocs from AliasesCSSProperties.

interface StyledSystemSpaceProps {
    * The **`margin`** CSS property sets the margin area on all four sides of an element. It is a shorthand for `margin-top`, `margin-right`, `margin-bottom`, and `margin-left`.
    * | Chrome | Firefox | Safari |  Edge  |  IE   |
    * | :----: | :-----: | :----: | :----: | :---: |
    * | **1**  |  **1**  | **1**  | **12** | **3** |
    * @see https://developer.mozilla.org/docs/Web/CSS/margin
  m: SystemCssProperties['m'];
    * The **`margin`** CSS property sets the margin area on all four sides of an element. It is a shorthand for `margin-top`, `margin-right`, `margin-bottom`, and `margin-left`.
    * | Chrome | Firefox | Safari |  Edge  |  IE   |
    * | :----: | :-----: | :----: | :----: | :---: |
    * | **1**  |  **1**  | **1**  | **12** | **3** |
    * @see https://developer.mozilla.org/docs/Web/CSS/margin
  margin: SystemCssProperties['margin'];

I’ll save myself the trouble and extend SpaceProps.

import { SpaceProps, ColorProps } from "styled-system";

export interface BoxProps extends SpaceProps, ColorProps {
  variant?: string;
  sx?: SxStyleProp;
  css?: Interpolation;
export const Box: React.FC<BoxProps>;

Okay, but Box is created with @emotion/styled so it should be StyledComponent

export interface BoxStyleProps extends SpaceProps, ColorProps {
  variant?: string;
  sx?: SxStyleProp;
  css?: Interpolation;
export const Box: StyledComponent<

We can use withComponent to substitute the div inside Box with something else.

const SectionBox = Box.withComponent("section");

And on top of it, we now support all div props, like contentEditable or tabIndex.

We get Flex for free. It’s just a Box with display: flex.

The Grid has width, columns and gap.

The Grid forwards ref to Box, so we have to check what forwardRef returns.

React.ForwardRefExoticComponent<React.PropsWithoutRef<P> & React.RefAttributes<T>>

Brilliant. Let’s alias it to ForwardRef<T, P>.

export interface BoxProps
  extends Omit<React.ComponentProps<"div">, "color" | "css">,
    BoxStyleProps {}
export interface GridProps extends BoxProps {
   * Minimum width of child elements
  width?: ResponsiveValue<string | number>;
   * 	Number of columns to use for the layout (cannot be used in conjunction with the width prop)
  columns?: ResponsiveValue<number>;
   * Space between child elements
  gap?: ResponsiveValue<string | number>;
export const Grid: ForwardRef<HTMLDivElement, GridProps>;

“Cannot be used in conjunction” suggests a union type, but I’m afraid of TS2589 so I’ll pass.


It’s getting a bit late already, so I’ll add a bit more and do the PR.

export interface ButtonProps
  extends Assign<React.ComponentPropsWithRef<"button">, BoxStyleProps> {}
export const Button: ForwardRef<HTMLButtonElement, BoxProps>;

export interface LinkProps
  extends Assign<React.ComponentPropsWithRef<"a">, BoxStyleProps> {}
export const Link: ForwardRef<HTMLAnchorElement, LinkProps>;

export type TextProps = BoxProps;
export const Text: ForwardRef<HTMLDivElement, BoxProps>;

export interface HeadingProps
  extends Assign<React.ComponentPropsWithRef<"h2">, BoxStyleProps> {}
export const Heading: ForwardRef<HTMLHeadingElement, HeadingProps>;

Continuing from this point should be a bit more pleasant.

The PR was merged after a few days 🎉