Support Date and Temporal.Instant (#6)

* feat: Serialize Date

* feat: Serialize Temporal.Instant

* docs: Add serialization strategy

* docs: Move Motivation down in README

* Fix typo

README.md

@@ -15,34 +15,31 @@ See this test for the [serialization behavior](./test/serialization.test.ts).
 
 [URLSearchParams]: https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams
 
-## Motivation
-
-URL search parameters are strings, however the Seam API will parse parameters as complex types.
-The Seam SDK must accept the complex types as input and serialize these
-to search parameters in a way supported by the Seam API.
-
-There is no single standard for this serialization.
-This module establishes the serialization standard adopted by the Seam API.
-
-### Why not use [URLSearchParams](https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams)?
-
-- Passing a raw object to URLSearchParams has unpredictable serialization behavior.
-
-### Why not [qs](https://github.com/ljharb/qs)?
-
-- Not a zero-dependency module. Has quite a few dependency layers.
-- Impractile as a reference implementation.
-  qs enables complex, non-standard parsing and serialization,
-  which makes ensuing SDK parity much harder.
-  Similarly, this puts an unreasonable burden on user's of the HTTP API or those implementing their own client.
-- The Seam API must ensure it handles a well defined set of non-string query parameters consistency.
-  Using qs would allow the SDK to send unsupported or incorrectly serialized parameter types to the API
-  resulting in unexpected behavior.
-
-### Why not use the default [Axios](https://axios-http.com/) serializer?
-
-- Using the default [Axios] serializer was the original approach,
-  however it had similar issues to using URLSearchParams and qs as noted above.
+### Serialization strategy
+
+Serialization uses
+[`URLSearchParams.toString()`](https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams/toString#return_value)
+which encodes most non-alphanumeric characters.
+
+- The primitive types `string`, `number`, and `bigint` are serialized using `.toString()`.
+- The primitive `boolean` type is serialized using `.toString()` to `'true'` or `'false'`.
+- The primitive `null` and `undefined` values are removed,
+  e.g., `{ foo: null, bar: undefined, baz: 1 }` serializes to `baz=1`.
+- `Date` objects are detected and serialized using `Date.toISOString()`.
+- `Temporal.Instant` objects are detected and serialized by first converting them to `Date`
+  and then serializing the `Date` as above.
+- Arrays are serialized using
+  [`URLSearchParams.append()`](https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams/append):
+  - Array values are serialized as above.
+  - The array `{ foo: [1, 2] }` serializes to `foo=1&foo=2`.
+  - The single element array `{ foo: [1] }` serializes to `foo=1`.
+  - The empty array `{ foo: [] }` serializes to `foo=`.
+  - Serialization of the single element array containing the empty string is not supported
+    and will throw an `UnserializableParamError`.
+    Otherwise, the serialization of `{ foo: [''] }` would conflict with `{ foo: [] }`.
+    This serializer chooses to support the more common and more useful case of an empty array.
+- Serialization of functions or other objects is not supported
+  and will throw an `UnserializableParamError`.
 
 ## Installation
 
@@ -111,6 +108,35 @@ const { data } = await client.get('/search', {
 
 [Axios]: https://axios-http.com/
 
+## Motivation
+
+URL search parameters are strings, however the Seam API will parse parameters as complex types.
+The Seam SDK must accept the complex types as input and serialize these
+to search parameters in a way supported by the Seam API.
+
+There is no single standard for this serialization.
+This module establishes the serialization standard adopted by the Seam API.
+
+### Why not use [URLSearchParams](https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams)?
+
+- Passing a raw object to URLSearchParams has unpredictable serialization behavior.
+
+### Why not [qs](https://github.com/ljharb/qs)?
+
+- Not a zero-dependency module. Has quite a few dependency layers.
+- Impractical as a reference implementation.
+  qs enables complex, non-standard parsing and serialization,
+  which makes ensuing SDK parity much harder.
+  Similarly, this puts an unreasonable burden on user's of the HTTP API or those implementing their own client.
+- The Seam API must ensure it handles a well defined set of non-string query parameters consistency.
+  Using qs would allow the SDK to send unsupported or incorrectly serialized parameter types to the API
+  resulting in unexpected behavior.
+
+### Why not use the default [Axios](https://axios-http.com/) serializer?
+
+- Using the default [Axios] serializer was the original approach,
+  however it had similar issues to using URLSearchParams and qs as noted above.
+
 ## Development and Testing
 
 ### Quickstart

package.json

@@ -68,6 +68,7 @@
     "npm": ">= 9.0.0"
   },
   "devDependencies": {
+    "@js-temporal/polyfill": "^0.4.4",
     "@types/node": "^20.8.10",
     "ava": "^6.0.1",
     "axios": "^1.6.5",

src/lib/date.ts

@@ -0,0 +1,32 @@
+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
+}
+
+interface TemporalInstantLike {
+  epochMilliseconds: number
+}
+
+export const isTemporalInstantLike = (v: unknown): v is TemporalInstantLike => {
+  if (v == null) return false
+  if (typeof v !== 'object') return false
+  if (!('epochMilliseconds' in v)) return false
+  try {
+    if (typeof v.epochMilliseconds !== 'number') return false
+    if (isNaN(v.epochMilliseconds)) return false
+    return true
+  } catch {
+    return false
+  }
+}

src/lib/serialize.ts

@@ -1,3 +1,5 @@
+import { isDateLike, isTemporalInstantLike } from './date.js'
+
 type Params = Record<string, unknown>
 
 export const serializeUrlSearchParams = (params: Params): string => {
@@ -38,6 +40,10 @@ 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()
+  if (isTemporalInstantLike(v)) {
+    return new Date(v.epochMilliseconds).toISOString()
+  }
   throw new UnserializableParamError(k, `is a ${typeof v}`)
 }
 

test/serialization.test.ts

@@ -1,3 +1,4 @@
+import { Temporal } from '@js-temporal/polyfill'
 import test from 'ava'
 
 import {
@@ -75,6 +76,24 @@ 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.only('serializes Temporal.Instant', (t) => {
+  t.is(
+    serializeUrlSearchParams({
+      foo: 1,
+      now: Temporal.Instant.fromEpochMilliseconds(1740422679000),
+    }),
+
+    'foo=1&now=2025-02-24T18%3A44%3A39.000Z',
+  )
+})
+
 test('cannot serialize unserializable values', (t) => {
   t.throws(() => serializeUrlSearchParams({ foo: {} }), {
     instanceOf: UnserializableParamError,