How to override Next.js `*.svg` module declaration?

Question

Next.js has recently made a modification (in v11.0.x) which has the following type definitions:

In next-env.d.ts (non-modifiable, regenerated at every build):

/// <reference types="next" />
/// <reference types="next/types/global" />
/// <reference types="next/image-types/global" />

In node_modules/next/image-types/global.d.ts (non-modifiable, don't wanna use patch-package):

declare module '*.svg' {
  const content: any
  export default content
}

Now the issue is that I am using @svgr/webpack, and as a result I need to do the following:

declare module '*.svg' {
  const content: React.FC<React.SVGAttributes<SVGElement>>
  export default content
}

Earlier placing this code in index.d.ts in the assets folder used to work. But now it doesn't and as result I am forced to cast every import separately. Any way to do this directly?

Answer 1

An alternative to replacing next-env.d.ts is to add an additional declarations file, e.g. additional.d.ts, as described in https://nextjs.org/docs/basic-features/typescript.

As noted in the docs, this file must be included in the include array of your tsconfig.json file, but I've found the order is important as well - the additional file must be included before next-env.d.ts.

This seems to be because when there are multiple declarations for the same module containing default exports, the first declaration wins.

// additional.d.ts
declare module "*.svg" {
  import React from "react";

  const content: React.FunctionComponent<React.SVGProps<SVGSVGElement>>;

  export default content;
}

// tsconfig.json
{
  "include": ["additional.d.ts", "next-env.d.ts"] // The order matters!
}

This gives our preferred type for SVGs, whilst preserving the other desirable behaviour from next-env.d.ts.

This seems preferable to simply replacing the built-in types file as the Next team have reserved the right to adjust the types in future, meaning the copied types would be need to manually be kept up-to-date, and this approach doesn't seem to be a documented approach.

Answer 2

I am using the following workaround:

• Add next-env.d.ts to exclude array in tsconfig.json:

  {
    // ...
    "exclude": ["node_modules", "next-env.d.ts"]
  }
  

• Add next-env.d.ts to .gitignore/.eslintignore.

• Create new file custom.d.ts:

  /// <reference types="next" />
  /// <reference types="next/types/global" />
  
  // additional things that one used to put here before Next.js v11
  

• Create new file images.d.ts:

  type StaticImageData = {
    src: string;
    height: number;
    width: number;
    placeholder?: string;
  };
  
  declare module '*.png' {
    const content: StaticImageData;
    export default content;
  }
  
  declare module '*.svg' {
    const content: React.FC<React.SVGProps<SVGSVGElement>>;
    export default content;
  }
  
  declare module '*.jpg' {
    const content: StaticImageData;
    export default content;
  }
  
  declare module '*.jpeg' {
    const content: StaticImageData;
    export default content;
  }
  
  declare module '*.gif' {
    const content: StaticImageData;
    export default content;
  }
  
  declare module '*.webp' {
    const content: StaticImageData;
    export default content;
  }
  
  declare module '*.ico' {
    const content: StaticImageData;
    export default content;
  }
  
  declare module '*.bmp' {
    const content: StaticImageData;
    export default content;
  }
  

• Make sure that these files are handled by patterns specified in include array of tsconfig.

• Add declarations for *.avif too if you're using them in next@12:

  declare module '*.avif' {
    const content: StaticImageData
    export default content
  }