如何在 TypeScript 中覆盖标准库 function 的类型？

Question

I'm working on a polyfill that extends the behavior of the JSON.parse() function by adding an optional third argument to the reviver callback function.

The polyfill should be imported like this for the end users:

import 'my-polyfill';

The JSON.parse() is defined in the node_modules/typescript/lib/lib.es5.d.ts like this:

// lib.es5.d.ts

interface JSON {

  // …

  parse(
    text: string,
    reviver?: (this: any, key: string, value: any) => any
  ): any;

  // …

}

How do I override this definition, so when the polyfill is installed/imported my definition is used instead? Eg:

interface ContextType {
  // …
}

interface JSON {

  parse<Type = any>(
    text: string,
    reviver?: (
      key: string,
      value: any,
      context?: ContextType
    ) => any

  ): Type;

}

Answer 1

You could create declarations file and name it, for example, as polyfill.d.ts . Then, you should use standard way of extending global types as follows:

declare global {
  interface JSON {
    // Here, you should write your own implementation of `parse` function.
    parse(variable: string): void;
  }
}

export {};

export is required by TypeScript and you can learn more about it in this answer and its comments.

Don't forget, that when you create a separate library, this file should exist in final build directory. So, when some user installs your package and imports it, file polyfill.d.ts would be automatically applied by TypeScript.

I am not sure, that you are able to make TypeScript transfer declarations file ( .d.ts ) with its own functionality. To do this, we should use some hack, described here . We should name file not polyfill.d.ts , but polyfill.ts and import it in library's index.ts file, so it would be imported by TypeScript and transferred to build directory.