Adding overload to method of built-in object in TypeScript

Question

A library I'm working with adds secondary functionality to JSON.parse, which is of course a built-in method on a built-in object (but writable). I need to add the following overload signature to let the TypeScript compiler know about the new functionality:

<T>(text: string, type: { new (): T }) => T

Obviously, I would refrain from touching lib.d.ts.

I tried redeclaring the entire JSON interface, as well as making the global JSON variable of that type, but that duplicated all built-in call signatures besides adding the new one.

If I redeclare the JSON interface with just the new signature, the whole thing seems to work correctly, the new method overload is accepted along with the built-in ones, but this just seems hackish and fragile:

declare interface JSON {
    parse<T>(text: string, type: { new (): T }): T;
}

declare var JSON: JSON;

How do I correctly extend a built-in object with a method overload?

basarat · Accepted Answer · 2016-04-12 03:04:27Z

3

Create a file globals.d.ts and just put in the following :

declare interface JSON {
    parse<T>(text: string, type: { new (): T }): T;
}

Now you can use this JSON.parse overload in yourfile.ts.

More

https://basarat.gitbooks.io/typescript/content/docs/types/lib.d.ts.html

answered Apr 12, 2016 at 3:04

basarat

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