feat: Serialize Date

Author: razor-x

src/lib/date.ts

@@ -0,0 +1,15 @@
+interface DateLike {
+  toISOString: () => string
+}
+
+export const isDateLike = (v: unknown): v is DateLike => {
+  if (v == null) return false
+  if (typeof v !== 'object') return false
+  if (
+    v instanceof Date ||
+    Object.prototype.toString.call(v) === '[object Date]'
+  ) {
+    return 'toISOString' in v
+  }
+  return false
+}

src/lib/serialize.ts

@@ -1,3 +1,5 @@
+import { isDateLike } from './date.js'
+
 type Params = Record<string, unknown>
 
 export const serializeUrlSearchParams = (params: Params): string => {
@@ -38,6 +40,7 @@ const serialize = (k: string, v: unknown): string => {
   if (typeof v === 'number') return v.toString()
   if (typeof v === 'bigint') return v.toString()
   if (typeof v === 'boolean') return v.toString()
+  if (isDateLike(v)) return v.toISOString()
   throw new UnserializableParamError(k, `is a ${typeof v}`)
 }
 

test/serialization.test.ts

@@ -75,6 +75,13 @@ test('cannot serialize single element array params with empty string', (t) => {
   })
 })
 
+test('serializes Date', (t) => {
+  t.is(
+    serializeUrlSearchParams({ foo: 1, now: new Date(1740422679000) }),
+    'foo=1&now=2025-02-24T18%3A44%3A39.000Z',
+  )
+})
+
 test('cannot serialize unserializable values', (t) => {
   t.throws(() => serializeUrlSearchParams({ foo: {} }), {
     instanceOf: UnserializableParamError,