How to extend Material-UI Theme with Typescript?

Question

Typescript is always complaining about certain properties missing in the palette. My app works just fine if I add //@ts-ignore, but I obviously want to avoid that. I'm new to Typescript and here is what I've tried.

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

interface IPaletteOptions extends PaletteOptions {
    chip: {
      color: string,
      expandIcon: {
        background: string,
        color: string,
      },
    },
}
interface ITheme extends Theme {
  palette: IPaletteOptions,
}

const theme: ITheme = createMuiTheme({
  typography: {
    fontWeightMedium: 600,
    fontFamily: ['Open Sans', 'Arial', 'sans-serif'].join(','),
  },
  palette: {
    primary: {
      main: '#43C099',
    },
    secondary: {
      main: '#7AF3CA',
    },
    chip: {
      color: '#C2C3C6',
      expandIcon: {
        background: '#808183',
        color: '#FFFFFF',
      },
    },
  },
} as ThemeOptions);

This throws an error,

Type 'Theme' is not assignable to type 'ITheme'.
  Types of property 'palette' are incompatible.
    Property 'chip' is missing in type 'Palette' but required in type 'IPaletteOptions

This is a confusing error for me, because type I'm not using the type Palette anywhere.

How can I properly extend the palette here?

Answer 1

This can be solved much easier via Module Augmentation:

MUI v5

material-ui.d.ts

import { PaletteOptions } from "@mui/material/styles/createPalette";

declare module "@mui/material/styles/createPalette" {
  export interface PaletteOptions {
    chip: {
      color: string;
      expandIcon: {
        background: string;
        color: string;
      };
    };
  }
}

MUI v4

material-ui.d.ts

import { PaletteOptions } from "@material-ui/core/styles/createPalette";

declare module "@material-ui/core/styles/createPalette" {
  export interface PaletteOptions {
    chip: {
      color: string;
      expandIcon: {
        background: string;
        color: string;
      };
    };
  }
}

Answer 2

Solution

import createMuiTheme, { Theme, ThemeOptions } from "@material-ui/core/styles/createMuiTheme";
import { Palette } from "@material-ui/core/styles/createPalette";

interface IPalette extends Palette {
  xxx: {}
}
interface ITheme extends Theme {
  palette: IPalette;
}
interface IThemeOptions extends ThemeOptions {
  palette: IPalette;
}

const theme = createMuiTheme({
  palette: {
    ...
    xxx: {}                                        // Type been checked
  }
} as IThemeOptions)                                // Use customized ThemeOptions type

const useStyles = makeStyles((theme: ITheme) => ({ // Use customized Theme type
  root: {
    color: theme.palette.xxx                       // Work with no type error
  }
}));

---

Refer

If we look at the createMuiTheme.d.ts

import { Palette, PaletteOptions } from './createPalette';

export interface ThemeOptions {
  palette?: PaletteOptions;
  ...
}

export interface Theme {
  palette: Palette;
  ...
}

export default function createMuiTheme(options?: ThemeOptions, ...args: object[]): Theme;

We would find that Theme and ThemeOptions play a different role.

• Theme: return type
• ThemeOptions: params type