allow passing null to JSON.parse()

[ImLunaHey]

Currently this fails type checking yet it works in all js environments I've tried.

JSON.parse(localStorage.getItem('a'));

[ImLunaHey]

Currently the annoying hack i need to use is JSON.parse(localStorage.getItem('a') || 'null');

[qb20nh]

JSON.parse does call ToString(argument) before actual parse begins.

https://tc39.es/ecma262/multipage/structured-data.html#sec-json.parse

1. Let jsonString be ? ToString(text).

Following cases are where ToString returns valid JSON values.
https://tc39.es/ecma262/multipage/abstract-operations.html#sec-tostring

4. If argument is null, return "null".
5. If argument is true, return "true".
6. If argument is false, return "false".
7. If argument is a Number, return Number::toString(argument, 10).
8. If argument is a BigInt, return BigInt::toString(argument, 10).

[ImLunaHey]

localStorage.setItem('a', null);
const result = JSON.parse(localStorage.getItem('a'));
console.log(result === null)
// true

localStorage.setItem('a', "null");
const result = JSON.parse(localStorage.getItem('a'));
console.log(result === null)
// true

[qb20nh]

The purpose is not to make every non throwing ECMAscript code pass typescript checking.

[ImLunaHey]

ts-reset smooths over these hard edges

[NoamAnisfeld]

I think JSON.parse typing should indeed only accept strings by default, because this is what most users would expect as "type-safe".

If one wants to get advantage of string coercion this can be easily done by JSON.parse(String(value)), no need to use value-specific hacks like || 'null'.

[ImLunaHey]

@NoamAnisfeld that makes it less typesafe. Typesafety should reflect what actually happens.