From e1af14e38e7b0956a6557bc4ba61c41cf67cba2e Mon Sep 17 00:00:00 2001
From: Darcy Parker <darcyparker@gmail.com>
Date: Thu, 4 Nov 2021 12:04:57 -0400
Subject: [PATCH 1/2] Jsonify: handle undefined in array.

---
 source/jsonify.d.ts |  9 ++++++++-
 test-d/jsonify.ts   | 14 +++++++++++++-
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/source/jsonify.d.ts b/source/jsonify.d.ts
index bc69492a8..eded0a98d 100644
--- a/source/jsonify.d.ts
+++ b/source/jsonify.d.ts
@@ -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.
 
@@ -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?
diff --git a/test-d/jsonify.ts b/test-d/jsonify.ts
index 691fdcd08..bc6889727 100644
--- a/test-d/jsonify.ts
+++ b/test-d/jsonify.ts
@@ -1,4 +1,4 @@
-import {expectAssignable, expectNotAssignable} from 'tsd';
+import {expectAssignable, expectNotAssignable, expectType} from 'tsd';
 import {Jsonify, JsonValue} from '..';
 
 interface A {
@@ -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);
+expectAssignable<JsonValue>(parsedStringifiedArrayWithUndefined1);
+expectNotAssignable<JsonValue>([undefined, 1]);
+declare const parsedStringifiedArrayWithUndefined2: Jsonify<[undefined, number]>;
+expectType<Array<number | null>>(parsedStringifiedArrayWithUndefined2);
+expectAssignable<JsonValue>(parsedStringifiedArrayWithUndefined2);

From 68474d1fd432c0ee16a94ab0a76bc65da179dba8 Mon Sep 17 00:00:00 2001
From: Darcy Parker <945058+darcyparker@users.noreply.github.com>
Date: Tue, 22 Mar 2022 08:04:02 -0400
Subject: [PATCH 2/2] jsonify.ts: Update to test more general
 Jsonify<undefined[]>.

---
 test-d/jsonify.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test-d/jsonify.ts b/test-d/jsonify.ts
index 5d0cda481..dd51f51cb 100644
--- a/test-d/jsonify.ts
+++ b/test-d/jsonify.ts
@@ -127,7 +127,7 @@ expectNotAssignable<JsonValue>(nonJsonWithInvalidToJSON.toJSON());
 // `[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]));
+declare const parsedStringifiedArrayWithUndefined1: Jsonify<undefined[]>; // = JSON.parse(JSON.stringify([undefined]));
 expectType<null[]>(parsedStringifiedArrayWithUndefined1);
 expectAssignable<JsonValue>(parsedStringifiedArrayWithUndefined1);
 expectNotAssignable<JsonValue>([undefined, 1]);