fix: Make slice compatible with all types of collections

__tests__/slice.js

@@ -1,9 +1,109 @@
 const slice = require('../src/slice')
 
+const object = {
+  'hello': 'Hello',
+  'bonsoir': 'Bonsoir',
+  'elliott': 'Elliot',
+  'world': 'World',
+}
+const map = new Map(Object.entries(object))
+const array = Object.values(object)
+const set = new Set(array)
+const newObject = { bonsoir: 'Bonsoir', elliott: 'Elliot' }
+const newMap = new Map(Object.entries(newObject))
+const newArray = Object.values(newObject)
+const newSet = new Set(newArray)
+
+
 describe('slice', () => {
-  it('should retrieve a part of the input array', () => {
-    const words = ['Hello', 'Bonsoir', 'Elliot', 'World']
-    expect(slice(1, 3, words)).toEqual(['Bonsoir', 'Elliot'])
+  describe('it should retrieve a slice of the input collection', () => {
+    it('should retrieve a slice of the input array', () => {
+      expect(slice(1, 3, array)).toEqual(newArray)
+    })
+
+    it('should retrieve a slice of the input set', () => {
+      expect(slice(1, 3, set)).toEqual(newSet)
+    })
+
+    it('should retrieve a slice of the input map', () => {
+      expect(slice(1, 3, map)).toEqual(newMap)
+    })
+
+    it('should retrieve a slice of the input object', () => {
+      expect(slice(1, 3, object)).toEqual(newObject)
+    })
+  })
+
+  describe('it should start from the end if the first parameter is negative', () => {
+    it('should retrieve a slice of the input array', () => {
+      expect(slice(-3, 3, array)).toEqual(newArray)
+    })
+
+    it('should retrieve a slice of the input set', () => {
+      expect(slice(-3, 3, set)).toEqual(newSet)
+    })
+
+    it('should retrieve a slice of the input map', () => {
+      expect(slice(-3, 3, map)).toEqual(newMap)
+    })
+
+    it('should retrieve a slice of the input object', () => {
+      expect(slice(-3, 3, object)).toEqual(newObject)
+    })
+  })
+
+  describe('it should start from the end if the second parameter is negative', () => {
+    it('should retrieve a slice of the input array', () => {
+      expect(slice(1, -1, array)).toEqual(newArray)
+    })
+
+    it('should retrieve a slice of the input set', () => {
+      expect(slice(1, -1, set)).toEqual(newSet)
+    })
+
+    it('should retrieve a slice of the input map', () => {
+      expect(slice(1, -1, map)).toEqual(newMap)
+    })
+
+    it('should retrieve a slice of the input object', () => {
+      expect(slice(1, -1, object)).toEqual(newObject)
+    })
+  })
+
+  describe('it should work if both start and end are negative', () => {
+    it('should retrieve a slice of the input array', () => {
+      expect(slice(-3, -1, array)).toEqual(newArray)
+    })
+
+    it('should retrieve a slice of the input set', () => {
+      expect(slice(-3, -1, set)).toEqual(newSet)
+    })
+
+    it('should retrieve a slice of the input map', () => {
+      expect(slice(-3, -1, map)).toEqual(newMap)
+    })
+
+    it('should retrieve a slice of the input object', () => {
+      expect(slice(-3, -1, object)).toEqual(newObject)
+    })
+  })
+
+  describe('it should return an empty collection if no results are found', () => {
+    it('should retrieve a slice of the input array', () => {
+      expect(slice(-3, 1, array)).toEqual([])
+    })
+
+    it('should retrieve a slice of the input set', () => {
+      expect(slice(-3, 1, set)).toEqual(new Set())
+    })
+
+    it('should retrieve a slice of the input map', () => {
+      expect(slice(-3, 1, map)).toEqual(new Map([]))
+    })
+
+    it('should retrieve a slice of the input object', () => {
+      expect(slice(-3, 1, object)).toEqual({})
+    })
   })
 
   it('should be a pure function', () => {

src/slice.js

@@ -1,5 +1,9 @@
 const curry = require('./curry')
+const dump = require('./dump')
+const length = require('./length')
 
-const slice = (start, end, array) => array.slice(start, end)
+const sliceTransformer = (start, end) => reducer => (acc, item, key, collection, index) => index >= start && index < end ? reducer(acc, item, key, collection, index) : acc
+
+const slice = (start, end, collection) => typeof collection.__proto__.slice === 'function' ?  collection.slice(start, end) : dump(sliceTransformer(start < 0 ? start + length(collection) : start, end < 0 ? end + length(collection) : end), collection)
 
 module.exports = curry(slice)