feat(guards): isUndefined

Signed-off-by: Lexus Drumgold <[email protected]>

src/guards/__tests__/is-undefined.spec-d.ts

@@ -0,0 +1,12 @@
+/**
+ * @file Type Tests - isUndefined
+ * @module tutils/guards/tests/unit-d/isUndefined
+ */
+
+import type testSubject from '../is-undefined'
+
+describe('unit-d:guards/isUndefined', () => {
+  it('should guard undefined', () => {
+    expectTypeOf<typeof testSubject>().guards.toBeUndefined()
+  })
+})

src/guards/__tests__/is-undefined.spec.ts

@@ -0,0 +1,16 @@
+/**
+ * @file Unit Tests - isUndefined
+ * @module tutils/guards/tests/unit/isUndefined
+ */
+
+import testSubject from '../is-undefined'
+
+describe('unit:guards/isUndefined', () => {
+  it('should return false if value is not undefined', () => {
+    expect(testSubject(faker.datatype.array())).to.be.false
+  })
+
+  it('should return true if value is undefined', () => {
+    expect(testSubject(undefined)).to.be.true
+  })
+})

src/guards/index.ts

@@ -17,3 +17,4 @@ export { default as isNIL } from './is-nil'
 export { default as isNodeEnv } from './is-node-env'
 export { default as isNull } from './is-null'
 export { default as isNumber } from './is-number'
+export { default as isUndefined } from './is-undefined'

src/guards/is-nil.ts

@@ -5,6 +5,7 @@
 
 import type { NIL } from '#src/types'
 import isNull from './is-null'
+import isUndefined from './is-undefined'
 
 /**
  * Checks if the given `value` is `null` or `undefined`.
@@ -13,7 +14,7 @@ import isNull from './is-null'
  * @return {value is NIL} `true` if `value` is {@linkcode NIL}
  */
 const isNIL = (value: unknown): value is NIL => {
-  return isNull(value) || value === undefined
+  return isNull(value) || isUndefined(value)
 }
 
 export default isNIL

src/guards/is-undefined.ts

@@ -0,0 +1,14 @@
+/**
+ * @file Type Guards - isUndefined
+ * @module tutils/guards/isUndefined
+ */
+
+/**
+ * Checks if the given `value` is `undefined`.
+ *
+ * @param {unknown} value - Value to evaluate
+ * @return {value is undefined} `true` if `value` is `undefined`
+ */
+const isUndefined = (value: unknown): value is undefined => value === undefined
+
+export default isUndefined