feat: add isRegExp function (#77)

benchmarks/typed/isRegExp.bench.ts

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

docs/typed/isRegExp.mdx

@@ -0,0 +1,17 @@
+---
+title: isRegExp
+description: Returns true for RegExp instances
+---
+
+## Basic usage
+
+Returns true for `RegExp` 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'
+
+_.isRegExp(/.+/) // true
+_.isRegExp(new RegExp('.+')) // true
+_.isRegExp(new (class extends RegExp {})('.+')) // true
+```

src/mod.ts

@@ -109,6 +109,7 @@ export * from './typed/isObject.ts'
 export * from './typed/isPlainObject.ts'
 export * from './typed/isPrimitive.ts'
 export * from './typed/isPromise.ts'
+export * from './typed/isRegExp.ts'
 export * from './typed/isString.ts'
 export * from './typed/isSymbol.ts'
 export * from './typed/isTagged.ts'

src/typed/isRegExp.ts

@@ -0,0 +1,5 @@
+import { isTagged } from 'radashi'
+
+export function isRegExp(value: unknown): value is RegExp {
+  return isTagged(value, '[object RegExp]')
+}

tests/typed/isRegExp.test.ts

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