Please provide a `json` basic type

Hi,

JSON is an important data exchange format. At present there is no explicit way to annotate an object as pure JSON. We were expecting union types to solve this problem via the following:

    interface Json {
        [x: string]: string|number|boolean|Date|Json|JsonArray;
    }
    interface JsonArray extends Array<string|number|boolean|Date|Json|JsonArray> { }

There are currently a number of problems with this.

• Contextual typing is absent in parenthetic expression #920

    interface Id extends Json {
        id: number;
    }
  
    var z = (): Id => ({id: 'foo'}); // Error: Missing index signature
  

• Contextual typing does not flow from base to subclasses #1373

class Bass {

    f(): Id{ return undefined;}
}

 // Error: missing index signature
class Foo extends Bass {
    f() { return { id: 10 }} 
}

• Object literals require explicit index signatures #1889:

    interface Foo extends Json {

        foo: { val: string }; // Error: Not assignable

    }

• Other problems:

  // Error: Missing index signature
  var result: Id[] = 'a|b'.split('|').map(item => {
        return { id: 0 };
  });
  

The first two problems look likely to be resolved, but not the last two.

This motivates the introduction of a natively supported json type that conforms to the JSON spec.

It should be possible to derive a custom JSON object from the json type with non of the problems above. Furthermore, since JSON is a data exchange format it should be possible to mark fields as nullable on types deriving from json (which would trigger a type guard).

I am of course aware that this is all rather vague!

[AlicanC]

Since when JSONs are objects?

type Json = string;

[AlicanC]

Yes, the JSON becomes an object and it’s not JSON anymore. JSON is what you give to JSON.parse(), not what you get from it. What you get is a value. Maybe you guys should rename your types to JsonValue.