feat(guards): isNIL

src/guards/__tests__/is-nil.guard.spec.ts

@@ -0,0 +1,28 @@
+import type { Testcase } from '@tests/utils/types'
+import testSubject from '../is-nil.guard'
+
+/**
+ * @file Unit Tests - isNIL
+ * @module tutils/guards/tests/unit/isNIL
+ */
+
+describe('unit:guards/isNIL', () => {
+  type Case = Testcase<boolean> & { state: string; value: any }
+
+  const cases: Case[] = [
+    { expected: false, state: 'boolean', value: true },
+    { expected: false, state: 'number', value: 13 },
+    { expected: false, state: 'object', value: { data: 26 } },
+    { expected: false, state: 'string', value: 'string' },
+    { expected: true, state: 'null', value: null },
+    { expected: true, state: 'undefined', value: undefined }
+  ]
+
+  it.each<Case>(cases)('should return $expected given $state', testcase => {
+    // Arrange
+    const { expected, value } = testcase
+
+    // Act + Expect
+    expect(testSubject(value)).toBe(expected)
+  })
+})

src/guards/index.ts

@@ -3,4 +3,5 @@
  * @module tutils/guards
  */
 
+export { default as isNIL } from './is-nil.guard'
 export { default as isNodeEnv } from './is-node-env.guard'

src/guards/is-nil.guard.ts

@@ -0,0 +1,18 @@
+import { NIL } from '@tutils/types'
+
+/**
+ * @file Type Guards - isNIL
+ * @module tutils/guards/isNIL
+ */
+
+/**
+ * Checks if `value` is a {@link NIL}.
+ *
+ * @param {any} [value] - Value to check
+ * @return {boolean} `true` if `value` is `null` or `undefined`
+ */
+const isNIL = (value?: any): value is NIL => {
+  return value === null || value === undefined
+}
+
+export default isNIL