feat(utils): add isNull, isUndefined & exists helpers

lib/utils/index.js

@@ -26,3 +26,9 @@ export const classNames = (...args) => {
 };
 
 export const mockState = (state, action) => ({ ...state, ...action });
+
+export const isUndefined = v => typeof v === 'undefined';
+
+export const isNull = v => v === null;
+
+export const exists = v => !isNull(v) && !isUndefined(v);

lib/utils/index.test.js

@@ -1,8 +1,7 @@
-import { classNames, mockState } from './';
+import { classNames, mockState, exists, isUndefined, isNull } from './';
 
 describe('utils', () => {
   describe('classNames(...classes)', () => {
-
     it('should merge arguments into a list of css classes', () => {
       expect(classNames('test', 'secondTest')).toBe('test secondTest');
     });
@@ -36,7 +35,6 @@ describe('utils', () => {
       expect(classNames('test', ['secondTest'], true))
         .toBe('test secondTest');
     });
-
   });
 
   describe('mockState(state, action)', () => {
@@ -45,4 +43,46 @@ describe('utils', () => {
         .toMatchObject({ foo: 'test' });
     });
   });
+
+  describe('isNull(value)', () => {
+    it('should return true when value is null', () => {
+      expect(isNull(null)).toBe(true);
+    });
+
+    it('should return false when value is undefined', () => {
+      expect(isNull()).toBe(false);
+    });
+
+    it('should return false when value is defined and not null', () => {
+      expect(isNull(true)).toBe(false);
+    });
+  });
+
+  describe('isUndefined(value)', () => {
+    it('should return true when value is undefined', () => {
+      expect(isUndefined()).toBe(true);
+    });
+
+    it('should return false when value is null', () => {
+      expect(isUndefined(null)).toBe(false);
+    });
+
+    it('should return false when value is defined and not null', () => {
+      expect(isUndefined(true)).toBe(false);
+    });
+  });
+
+  describe('exists(value)', () => {
+    it('should return true when value is defined and not null', () => {
+      expect(exists(0)).toBe(true);
+    });
+
+    it('should return false when value is null', () => {
+      expect(exists(null)).toBe(false);
+    });
+
+    it('should return false when value is not defined', () => {
+      expect(exists()).toBe(false);
+    });
+  });
 });