Fix serialization for Invalid/NaN dates

__tests__/index.test.ts

@@ -169,6 +169,16 @@ describe("simple serialization", () => {
     expect(deserialized).toBeInstanceOf(Uint8Array);
     expect(new Uint8Array(deserialized)).toStrictEqual(new Uint8Array(buf));
   })
+
+  it("preserves Invalid Date values through serialization", () => {
+    let invalidDate = new Date(NaN);
+    let serialized = serialize(invalidDate);
+    expect(serialized).toBe('["date",null]');
+
+    let deserialized = deserialize(serialized) as Date;
+    expect(deserialized).toBeInstanceOf(Date);
+    expect(Number.isNaN(deserialized.getTime())).toBe(true);
+  })
 });
 
 // =======================================================================================

src/serialize.ts

@@ -142,8 +142,10 @@ export class Devaluator {
       case "bigint":
         return ["bigint", (<bigint>value).toString()];
 
-      case "date":
-        return ["date", (<Date>value).getTime()];
+      case "date": {
+        const time = (<Date>value).getTime();
+        return ["date", Number.isNaN(time) ? null : time];
+      }
 
       case "bytes": {
         let bytes = value as Uint8Array;
@@ -496,6 +498,9 @@ export class Evaluator {
           }
           break;
         case "date":
+          if (value[1] === null) {
+            return new Date(NaN);
+          }
           if (typeof value[1] == "number") {
             return new Date(value[1]);
           }