feat: add isWeakMap function (#77)

benchmarks/typed/isWeakMap.bench.ts

@@ -0,0 +1,9 @@
+import * as _ from 'radashi'
+import { bench } from 'vitest'
+
+describe('isWeakMap', () => {
+  bench('with no arguments', () => {
+    _.isWeakMap()
+  })
+})
+

docs/typed/isWeakMap.mdx

@@ -0,0 +1,16 @@
+---
+title: isWeakMap
+description: Returns true for WeakMap instances
+---
+
+## Basic usage
+
+Returns true for `WeakMap` instances, even if they are subclass instances or from
+other [realms](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/instanceof#instanceof_and_multiple_realms).
+
+```ts
+import * as _ from 'radashi'
+
+_.isWeakMap(new WeakMap()) // true
+_.isWeakMap(new (class extends WeakMap {})()) // true
+```

src/mod.ts

@@ -114,6 +114,7 @@ export * from './typed/isSet.ts'
 export * from './typed/isString.ts'
 export * from './typed/isSymbol.ts'
 export * from './typed/isTagged.ts'
+export * from './typed/isWeakMap.ts'
 export * from './typed/isWeakSet.ts'
 
 export * from './types'

src/typed/isWeakMap.ts

@@ -0,0 +1,7 @@
+import { isTagged } from 'radashi'
+
+export function isWeakMap<K extends WeakKey = WeakKey, V = unknown>(
+  value: unknown,
+): value is WeakMap<K, V> {
+  return isTagged(value, '[object WeakMap]')
+}

tests/typed/isWeakMap.test.ts

@@ -0,0 +1,23 @@
+import * as vm from 'node:vm'
+import * as _ from 'radashi'
+
+describe('isWeakMap', () => {
+  test('returns true for WeakMap instances', () => {
+    expect(_.isWeakMap(new WeakMap())).toBe(true)
+  })
+  test('returns true for WeakMap subclass instances', () => {
+    expect(_.isWeakMap(new (class extends WeakMap {})())).toBe(true)
+  })
+  test('returns true for WeakMap instances from other realms', () => {
+    expect(_.isWeakMap(vm.runInNewContext('new WeakMap()'))).toBe(true)
+  })
+  test('returns false for undefined', () => {
+    expect(_.isWeakMap(undefined)).toBe(false)
+  })
+  test('returns false for null', () => {
+    expect(_.isWeakMap(null)).toBe(false)
+  })
+  test('returns false for non-WeakMap objects', () => {
+    expect(_.isWeakMap({})).toBe(false)
+  })
+})