Declare module

The declare module syntax in TypeScript is used to extend or add types to existing modules, especially when working with third-party libraries. Here are a few more examples of how you might use the declare module syntax:

Example 1: Extending a Third-Party Library

Suppose you’re working with a library called “awesome-library” that doesn’t have type definitions built-in. You can use declare module to add your own type definitions for the library’s components:

declare module 'awesome-library' {
    export function doSomething(value: string): void;
    export function doAnotherThing(): number;
}

Example 2: Extending a Module with Interfaces

Let’s say you’re using the “axios” library for making HTTP requests and you want to extend the types of its response data:

import axios, { AxiosResponse } from 'axios';

declare module 'axios' {
    interface AxiosResponse<T = any> {
        customData: T;
    }
}

// Now you can use your customData property in responses
axios.get('/api/data').then((response: AxiosResponse<{ customData: number }>) => {
    const data = response.customData;
});

Example 3: Extending a Module with Enums

If you’re using an enum from a library and want to add your own values:

declare module 'my-enums' {
    export enum Colors {
        Red = 'red',
        Green = 'green',
        Blue = 'blue',
        CustomColor = 'custom',
    }
}

Example 4: Extending the Window Object

You can extend the global window object to add new properties:

interface CustomWindow extends Window {
    myApp: {
        version: string;
    };
}

declare global {
    interface Window {
        myApp: {
            version: string;
        };
    }
}

// Now you can access your custom property on the window object
window.myApp.version = '1.0.0';

These examples demonstrate different scenarios where you might use declare module to add, extend, or modify types within existing modules or global objects. It’s a powerful feature of TypeScript that allows you to provide better type information and integrate with third-party libraries more effectively.

Extend type for mui color palette

// Augment the palette to include a violet color
declare module '@mui/material/styles' {
  interface Palette {
    violet: Palette['primary'];
  }

  interface PaletteOptions {
    violet?: PaletteOptions['primary'];
  }
}

The syntax you’re seeing is TypeScript’s way of referencing and reusing types within the same interface definition. Let me break down that specific part for clarity:

customNeutral: Palette['primary'];

In this line, you’re defining the customNeutral palette to be the same type as the primary palette. Here’s what it means in more straightforward terms:

• The Palette interface represents a color palette in Material-UI.
• The Palette['primary'] syntax is a way to refer to the type of the primary property within the Palette interface.

So, by using customNeutral: Palette['primary'], you’re saying that customNeutral will have the same type as the primary palette. This means that any properties you define within customNeutral will need to match the structure of the primary palette.

For example, in your code:

customNeutral: {
    light: grey[50],
    main: grey[200],
    dark: grey[700],
    contrastText: grey[900],
},

You’re structuring customNeutral to have the same properties (light, main, dark, contrastText) as the primary palette.

If you find this syntax confusing, you can make it more explicit by directly referencing the properties you want instead of using Palette['primary']. For instance:

customNeutral: {
    light: grey[50],
    main: grey[200],
    dark: grey[700],
    contrastText: grey[900],
} as PaletteColor,

Here, I’ve used PaletteColor to explicitly state the type, but you can replace it with the exact type that the primary palette properties have. This makes it clearer what you’re defining for customNeutral.

Remember, this syntax is specific to TypeScript and interfaces and is used to reuse and reference type definitions within an interface or type declaration.