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Jsonify: handle undefined in array. #310

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merged 3 commits into from Mar 30, 2022
Merged

Jsonify: handle undefined in array. #310

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e1af14e
Jsonify: handle undefined in array.
darcyparker Nov 4, 2021
d5aa142
Merge branch 'main' into JsonifyHandleUndefinedInArray
darcyparker Mar 22, 2022
68474d1
jsonify.ts: Update to test more general Jsonify<undefined[]>.
darcyparker Mar 22, 2022
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9 changes: 8 additions & 1 deletion source/jsonify.d.ts
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Expand Up @@ -3,6 +3,13 @@ import {JsonPrimitive, JsonValue} from './basic';
// Note: The return value has to be `any` and not `unknown` so it can match `void`.
type NotJsonable = ((...args: any[]) => any) | undefined;

// Note: Handles special case where Arrays with `undefined` are transformed to `'null'` by `JSON.stringify()`
// Only use with array members
type JsonifyArrayMember<T> =
T extends undefined ?
null | Exclude<T, undefined> :
Jsonify<T>;

/**
Transform a type to one that is assignable to the `JsonValue` type.

Expand Down Expand Up @@ -64,7 +71,7 @@ type Jsonify<T> =
? T extends JsonPrimitive
? T // Primitive is acceptable
: T extends Array<infer U>
? Array<Jsonify<U>> // It's an array: recursive call for its children
? Array<JsonifyArrayMember<U>> // It's an array: recursive call for its children
: T extends object
? T extends {toJSON(): infer J}
? (() => J) extends (() => JsonValue) // Is J assignable to JsonValue?
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14 changes: 13 additions & 1 deletion test-d/jsonify.ts
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@@ -1,4 +1,4 @@
import {expectAssignable, expectNotAssignable} from 'tsd';
import {expectAssignable, expectNotAssignable, expectType} from 'tsd';
import {Jsonify, JsonValue} from '..';

interface A {
Expand Down Expand Up @@ -122,3 +122,15 @@ class NonJsonWithInvalidToJSON {
const nonJsonWithInvalidToJSON = new NonJsonWithInvalidToJSON();
expectNotAssignable<JsonValue>(nonJsonWithInvalidToJSON);
expectNotAssignable<JsonValue>(nonJsonWithInvalidToJSON.toJSON());

// Special cases of Array with `undefined` member
// `[undefined]` is not JSON because it contains non JSON value `undefined`
// However `JSON.parse(JSON.stringify())` transforms array members of `undefined` to `null`
expectNotAssignable<JsonValue>([undefined]);
declare const parsedStringifiedArrayWithUndefined1: Jsonify<[undefined]>; // = JSON.parse(JSON.stringify([undefined]));
expectType<null[]>(parsedStringifiedArrayWithUndefined1);
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Since it's expecting null[], I think it should test Jsonify<undefined[]> for consistency.

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I am not sure what you mean.

I am verifying Jsonify<undefined[]> is the expected null[].

expectType<Jsonify<undefined[]>(parsedStringifiedArrayWithUndefined1); would be true if the implementation of Jsonify was wrong.

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I am verifying Jsonify<undefined[]> is the expected null[].

I am saying that it should do that. However, it currently doesn't test Jsonify<undefined[]>, it tests Jsonify<[undefined]>.

Ultimately it isn't a big deal, I just didn't see any point in using a tuple.

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Ah - I get what you're saying now. Thanks. I will make that correction when I get back to this problem.

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Addressed in 68474d1

expectAssignable<JsonValue>(parsedStringifiedArrayWithUndefined1);
expectNotAssignable<JsonValue>([undefined, 1]);
declare const parsedStringifiedArrayWithUndefined2: Jsonify<[undefined, number]>;
expectType<Array<number | null>>(parsedStringifiedArrayWithUndefined2);
expectAssignable<JsonValue>(parsedStringifiedArrayWithUndefined2);