create-react-app/packages/react-scripts/config/react-app.d.ts

// @remove-file-on-eject
// Do not edit this file. It's replaced every time you launch a toolbox action.
// If you need to add additional declarations, please do so in a new file.

declare namespace NodeJS {
  interface Process {
    env: {
      [key: string]: string | undefined;
      NODE_ENV: 'development' | 'production' | 'test';
      PUBLIC_URL: string;
    };
  }
}

declare module '*.bmp' {
  const src: string;
  export default src;
}

declare module '*.gif' {
  const src: string;
  export default src;
}

declare module '*.jpg' {
  const src: string;
  export default src;
}

declare module '*.jpeg' {
  const src: string;
  export default src;
}

declare module '*.png' {
  const src: string;
  export default src;
}

declare module '*.svg' {
  import * as React from 'react';

  export const ReactComponent: React.SFC<React.SVGProps<SVGSVGElement>>;

  const src: string;
  export default src;
}

declare module '*.module.css' {
  const classes: { [key: string]: string };
  export default classes;
}

declare module '*.module.scss' {
  const classes: { [key: string]: string };
  export default classes;
}

declare module '*.module.sass' {
  const classes: { [key: string]: string };
  export default classes;
}