TypeScript

You can add static typing to JavaScript to improve developer productivity and code quality thanks to TypeScript.

Have a look at the Create React App with TypeScript example. A minimum version of TypeScript 2.8 is required.

In order for types to work, you have to at least have the following options enabled in your tsconfig.json:

{
  "compilerOptions": {
    "lib": ["es6", "dom"],
    "noImplicitAny": true,
    "noImplicitThis": true,
    "strictNullChecks": true
  }
}

The strict mode options are the same that are required for every types package published in the @types/ namespace. Using a less strict tsconfig.json or omitting some of the libraries might cause errors. To get the best type experience with the types we recommend setting "strict": true.

Usage of withStyles

Using withStyles in TypeScript can be a little tricky, but there are some utilities to make the experience as painless as possible.

Using createStyles to defeat type widening

A frequent source of confusion is TypeScript's type widening, which causes this example not to work as expected:

const styles = {
  root: {
    display: 'flex',
    flexDirection: 'column',
  }
};

withStyles(styles);
//         ^^^^^^
//         Types of property 'flexDirection' are incompatible.
//           Type 'string' is not assignable to type '"-moz-initial" | "inherit" | "initial" | "revert" | "unset" | "column" | "column-reverse" | "row"...'.

The problem is that the type of the flexDirection property is inferred as string, which is too arbitrary. To fix this, you can pass the styles object directly to withStyles:

withStyles({
  root: {
    display: 'flex',
    flexDirection: 'column',
  },
});

However type widening rears its ugly head once more if you try to make the styles depend on the theme:

withStyles(({ palette, spacing }) => ({
  root: {
    display: 'flex',
    flexDirection: 'column',
    padding: spacing.unit,
    backgroundColor: palette.background.default,
    color: palette.primary.main,
  },
}));

This is because TypeScript widens the return types of function expressions.

Because of this, using the createStyles helper function to construct your style rules object is recommended:

// Non-dependent styles
const styles = createStyles({
  root: {
    display: 'flex',
    flexDirection: 'column',
  },
});

// Theme-dependent styles
const styles = ({ palette, spacing }: Theme) => createStyles({
  root: {
    display: 'flex',
    flexDirection: 'column',
    padding: spacing.unit,
    backgroundColor: palette.background.default,
    color: palette.primary.main,
  },
});

createStyles is just the identity function; it doesn't "do anything" at runtime, just helps guide type inference at compile time.

Media queries

withStyles allows a styles object with top level media-queries like so:

const styles = createStyles({
  root: {
    minHeight: '100vh',
  },
  '@media (min-width: 960px)': {
    root: {
      display: 'flex',
    },
  },
});

However to allow these styles to pass TypeScript, the definitions have to be ambiguous concerning names for CSS classes and actual CSS property names. Due to this class names that are equal to CSS properties should be avoided.

// error because TypeScript thinks `@media (min-width: 960px)` is a class name
// and `content` is the css property
const ambiguousStyles = createStyles({
  content: {
    minHeight: '100vh',
  },
  '@media (min-width: 960px)': {
    content: {
      display: 'flex',
    },
  },
});

// works just fine
const ambiguousStyles = createStyles({
  contentClass: {
    minHeight: '100vh',
  },
  '@media (min-width: 960px)': {
    contentClass: {
      display: 'flex',
    },
  },
});

Augmenting your props using WithStyles

Since a component decorated with withStyles(styles) gets a special classes prop injected, you will want to define its props accordingly:

const styles = (theme: Theme) => createStyles({
  root: { /* ... */ },
  paper: { /* ... */ },
  button: { /* ... */ },
});

interface Props {
  // non-style props
  foo: number;
  bar: boolean;
  // injected style props
  classes: {
    root: string;
    paper: string;
    button: string;
  };
}

However this isn't very DRY because it requires you to maintain the class names ('root', 'paper', 'button', ...) in two different places. We provide a type operator WithStyles to help with this, so that you can just write:

import { WithStyles, createStyles } from '@material-ui/core';

const styles = (theme: Theme) => createStyles({
  root: { /* ... */ },
  paper: { /* ... */ },
  button: { /* ... */ },
});

interface Props extends WithStyles<typeof styles> {
  foo: number;
  bar: boolean;
}

Decorating components

Applying withStyles(styles) as a function works as expected:

const DecoratedSFC = withStyles(styles)(({ text, type, color, classes }: Props) => (
  <Typography variant={type} color={color} classes={classes}>
    {text}
  </Typography>
));

const DecoratedClass = withStyles(styles)(
  class extends React.Component<Props> {
    render() {
      const { text, type, color, classes } = this.props
      return (
        <Typography variant={type} color={color} classes={classes}>
          {text}
        </Typography>
      );
    }
  }
);

Unfortunately due to a current limitation of TypeScript decorators, withStyles(styles) can't be used as a decorator in TypeScript.

Customization of Theme

When adding custom properties to the Theme, you may continue to use it in a strongly typed way by exploiting TypeScript's module augmentation.

The following example adds an appDrawer property that is merged into the one exported by material-ui:

import { Theme } from '@material-ui/core/styles/createMuiTheme';
import { Breakpoint } from '@material-ui/core/styles/createBreakpoints';

declare module '@material-ui/core/styles/createMuiTheme' {
  interface Theme {
    appDrawer: {
      width: React.CSSProperties['width']
      breakpoint: Breakpoint
    }
  }
  // allow configuration using `createMuiTheme`
  interface ThemeOptions {
    appDrawer?: {
      width?: React.CSSProperties['width']
      breakpoint?: Breakpoint
    }
  }
}

And a custom theme factory with additional defaulted options:

./styles/createMyTheme:

import createMuiTheme, { ThemeOptions } from '@material-ui/core/styles/createMuiTheme';

export default function createMyTheme(options: ThemeOptions) {
  return createMuiTheme({
    appDrawer: {
      width: 225,
      breakpoint: 'lg',
    },
    ...options,
  })
}

This could be used like:

import createMyTheme from './styles/createMyTheme';

const theme = createMyTheme({ appDrawer: { breakpoint: 'md' }});

Usage of component prop

Material-UI allows you to replace a component's root node via a component prop. For example, a Button's root node can be replaced with a React Router's Link, and any additional props that are passed to Button, such as to, will be spread to the Link component. For a code example concerning Button and react-router-dom checkout these demos.

Not every component fully supports any component type you pass in. If you encounter a component that rejects its component props in TypeScript please open an issue. There is an ongoing effort to fix this by making component props generic.

Handling value and event handlers

Many components concerned with user input offer a value prop or event handlers which include the current value. In most situations that value is only handled within React which allows it be of any type, such as objects or arrays.

However, that type cannot be verified at compile time in situations where it depends on the component's children e.g. for Select or RadioGroup. This means that the soundest option is to type it as unknown and let the developer decide how they want to narrow that type down. We do not offer the possibility to use a generic type in those cases for the same reasons event.target is not generic in React.

The demos include typed variants that use type casting. It is an acceptable tradeoff because the types are all located in a single file and are very basic. You have to decide for yourself if the same tradeoff is acceptable for you. The library types are be strict by default and loose via opt-in.