Allow optional shape entries

src/index.ts

@@ -149,11 +149,7 @@ export const Parse = {
       const result = {} as { [K in keyof T]: ReturnType<T[K]> };
 
       for (const key in parsers) {
-        if (!(key in val)) {
-          throw new ParseError(`Missing prop: ${key}`, shapeName);
-        }
-
-        const value = (val as Record<string, unknown>)[key];
+        const value = (val as Record<string, unknown>)[key] ?? undefined;
 
         try {
           // biome-ignore lint/style/noNonNullAssertion: Logically guaranteed

src/test/parse.test.ts

@@ -140,6 +140,33 @@ describe(Parse.shape, () => {
     const shape = { name: Parse.string, age: Parse.number };
     expect(() => Parse.shape(shape)(obj)).toThrow(ParseError);
   });
+
+  test("allows optional object entries", () => {
+    const parseThing = Parse.shape({
+      name: Parse.string,
+      another: Parse.optional(Parse.string),
+    });
+
+    const result = parseThing({
+      name: "hello",
+    });
+
+    expect(result).toEqual({
+      name: "hello",
+      another: undefined,
+    });
+  });
+
+  test("throws when a required value is missing", () => {
+    const parseThing = Parse.shape({
+      name: Parse.string,
+      another: Parse.optional(Parse.string),
+    });
+
+    expect(() => {
+      parseThing({ another: "hello" });
+    }).toThrow(ParseError);
+  });
 });
 
 describe(Parse.enum, () => {