feat: add decrement function and export types

src/functions/increment.spec.ts

@@ -1,4 +1,4 @@
-import {increment} from '../index'
+import {increment, decrement} from '../index'
 
 describe('Increment', () => {
   it('should increment', () => {
@@ -13,5 +13,11 @@ describe('Increment', () => {
     expect(counterTwo()).toBe(10)
     expect(counterTwo()).toBe(15)
     expect(counterTwo()).toBe(20)
+
+    const counterThree = decrement({initial: 10})
+
+    expect(counterThree()).toBe(10)
+    expect(counterThree()).toBe(9)
+    expect(counterThree()).toBe(8)
   })
 })

src/functions/increment.ts

@@ -1,3 +1,5 @@
+import {defaults} from './defaults'
+
 export interface IncrementOptions {
   /** Initial Value for the counter, defaults to `0` */
   initial: number
@@ -19,11 +21,16 @@ export type IncrementFunction = () => number
  * @returns `IncrementFunction`
  */
 export const increment = (
-  {initial, increment: incrementBy}: IncrementOptions = {
-    increment: 1,
-    initial: 0
-  }
+  options?: Partial<IncrementOptions>
 ): IncrementFunction => {
+  const {initial, increment: incrementBy} = defaults<IncrementOptions>(
+    options,
+    {
+      increment: 1,
+      initial: 0
+    }
+  )
+
   let counter = initial - incrementBy
 
   return () => {
@@ -32,3 +39,23 @@ export const increment = (
     return counter
   }
 }
+
+export const decrement = (
+  options: Partial<IncrementOptions>
+): IncrementFunction => {
+  const {initial, increment: incrementBy} = defaults<IncrementOptions>(
+    options,
+    {
+      increment: 1,
+      initial: 0
+    }
+  )
+
+  let counter = initial + incrementBy
+
+  return () => {
+    counter -= incrementBy
+
+    return counter
+  }
+}

src/index.ts

@@ -34,7 +34,12 @@ export {diffArray} from './functions/diff-array'
 export {diffObject} from './functions/diff-object'
 export {groupedBy, GroupedArray} from './functions/grouped-by'
 export {ifFn} from './functions/if-fn'
-export {increment} from './functions/increment'
+export {
+  increment,
+  IncrementFunction,
+  IncrementOptions,
+  decrement
+} from './functions/increment'
 export {indexedBy, IndexedArray, IndexedByOptions} from './functions/indexed-by'
 export {keys} from './functions/keys'
 export {mapProperty} from './functions/map-property'