metamask-extension/types/global.d.ts

// In order for variables to be considered on the global scope they must be
// declared using var and not const or let, which is why this rule is disabled
/* eslint-disable no-var */

declare class Platform {
  openTab: (opts: { url: string }) => void;

  closeCurrentWindow: () => void;
}
export declare global {
  var platform: Platform;
}