Use NullObject, restore isDate

src/index.ts

@@ -58,6 +58,12 @@ const domainValueRegExp =
  */
 const pathValueRegExp = /^[\u0020-\u003A\u003D-\u007E]*$/;
 
+const __toString = Object.prototype.toString;
+const __hasOwnProperty = Object.prototype.hasOwnProperty;
+
+const NullObject = function () {};
+NullObject.prototype = Object.create(null);
+
 /**
  * Parse options.
  */
@@ -86,7 +92,7 @@ export function parse(
   str: string,
   options?: ParseOptions,
 ): Record<string, string> {
-  const obj: Record<string, string> = {};
+  const obj: Record<string, string> = new NullObject();
   const len = str.length;
   // RFC 6265 sec 4.1.1, RFC 2616 2.2 defines a cookie name consists of one char minimum, plus '='.
   if (len < 2) return obj;
@@ -112,7 +118,7 @@ export function parse(
     const key = str.slice(keyStartIdx, keyEndIdx);
 
     // only assign once
-    if (!obj.hasOwnProperty(key)) {
+    if (!__hasOwnProperty.call(obj, key)) {
       let valStartIdx = startIndex(str, eqIdx + 1, endIdx);
       let valEndIdx = endIndex(str, endIdx, valStartIdx);
 
@@ -296,7 +302,10 @@ export function serialize(
   }
 
   if (options.expires) {
-    if (!Number.isFinite(options.expires.valueOf())) {
+    if (
+      !isDate(options.expires) ||
+      !Number.isFinite(options.expires.valueOf())
+    ) {
       throw new TypeError("option expires is invalid");
     }
 
@@ -358,6 +367,13 @@ function decode(str: string): string {
   return str.indexOf("%") !== -1 ? decodeURIComponent(str) : str;
 }
 
+/**
+ * Determine if value is a Date.
+ */
+function isDate(val: any): val is Date {
+  return __toString.call(val) === "[object Date]";
+}
+
 /**
  * Try decoding a string using a decoding function.
  */