From 4e37c4b75a2a0646a420201ef0c8197b6822ca07 Mon Sep 17 00:00:00 2001
From: akolarski <37934108+akolarski@users.noreply.github.com>
Date: Sun, 24 Jul 2022 22:49:54 +0300
Subject: [PATCH 1/2] Make parser check optional fields too.

When creating a Type Guard pass interface with all required fields to the parser but parser still returns the original interface.
---
 src/index.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/index.ts b/src/index.ts
index 8f9f9a6..2666971 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -5,7 +5,7 @@ function hasProperties<T extends object, K extends string>(obj: T, ...keys: K[])
 }
 
 
-const createTypeGuard = <T>(parse: Parser<T>) => (value: unknown): value is T => {
+const createTypeGuard = <T>(parse: Parser<Required<T>>) => (value: unknown): value is T => {
     return parse(value) !== null;
 };
 

From e02a62912337cd055cb64d2781084e5cddce1a14 Mon Sep 17 00:00:00 2001
From: akolarski <37934108+akolarski@users.noreply.github.com>
Date: Sun, 24 Jul 2022 23:14:55 +0300
Subject: [PATCH 2/2] A better approach is for the parser to require for the
 whole to be defined.

---
 src/index.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/index.ts b/src/index.ts
index 2666971..49710cf 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,11 +1,11 @@
-type Parser<T> = (value: unknown) => T | null;
+type Parser<T> = (value: unknown) => Required<T> | null;
 
 function hasProperties<T extends object, K extends string>(obj: T, ...keys: K[]): obj is T & { [J in K]: unknown } {
     return !!obj && keys.every(key => obj.hasOwnProperty(key));
 }
 
 
-const createTypeGuard = <T>(parse: Parser<Required<T>>) => (value: unknown): value is T => {
+const createTypeGuard = <T>(parse: Parser<T>) => (value: unknown): value is T => {
     return parse(value) !== null;
 };