#37 Add isEmpty into mappers

README.md

@@ -49,7 +49,7 @@ npm i xlsx-import --save
 Mapper is a function that transforms values. You can use [built-in mappers](#Mappers) or write your own
 
 ```ts
-    import { upperCaseMapper } from 'xlsx-import/lib/mappers';
+    import { upperCaseMapper, isEmpty } from 'xlsx-import/lib/mappers';
 
     const config = {
         // ...
@@ -59,6 +59,7 @@ Mapper is a function that transforms values. You can use [built-in mappers](#Map
             fields:[
                 {row: 2, col:1, key:'FirstName'},
                 {row: 2, col:2, key:'SecondName', mapper: upperCaseMapper},
+                {row: 2, col:3, key:'ArtistName', mapper: isEmpty},
                 {row: 3, col:1, key:'Age', mapper: Number.parseInt},
             ]
         },
@@ -123,6 +124,7 @@ This is `type` related configuration, for more information please study examples
 | Exported Name | Description
 |-----|-----------
 |upperCaseMapper|Transforms string to upper case
+|isEmpty|Examines if input is empty
 
 # See also
 

src/mappers/index.ts

@@ -3,3 +3,4 @@ import { stringMapper } from './stringMapper';
 /** probably `MAPPER_DEFAULT` should never be changed. Designed for internal usages when mapper isn't precised. */
 export const MAPPER_DEFAULT = stringMapper;
 export { upperCaseMapper } from './upperCaseMapper';
+export { isEmpty } from './isEmpty';

src/mappers/isEmpty.ts

@@ -0,0 +1,3 @@
+import { ValueMapper } from '../abstracts/ValueMapper';
+
+export const isEmpty: ValueMapper<boolean> = value => value == null || value === '';

tests/unit/mappers/stringMapper.test.ts

@@ -1,5 +1,5 @@
 import * as chai from 'chai';
-import { upperCaseMapper } from '../../../src/mappers';
+import { upperCaseMapper, isEmpty } from '../../../src/mappers';
 import { stringMapper } from '../../../src/mappers/stringMapper';
 
 describe('Mappers, unit tests', () => {
@@ -44,4 +44,20 @@ describe('Mappers, unit tests', () => {
           });
       });
   });
+
+  describe('isEmpty', () => {
+    const dataProvider = [
+        { inValue: '', expectedResult: true },
+        { inValue: null, expectedResult: true },
+        { inValue: ' ', expectedResult: false }, // it is quite problematic case, however it isn't empty
+        { inValue: 'null', expectedResult: false },
+        { inValue: 'a', expectedResult: false},
+        { inValue: 'as d', expectedResult: false },
+      ]
+      dataProvider.forEach(({inValue, expectedResult}) => {
+          it(`isEmpty for input "${inValue}" SHOULD return "${expectedResult}"`, () => {
+              chai.expect(isEmpty(inValue as string)).equal(expectedResult);
+          });
+      });
+  });
 });