fix(functions): add isNil and do not depend on nullish coallesce

.babelrc

@@ -1,5 +1,4 @@
 {
-  "plugins": ["@babel/plugin-proposal-nullish-coalescing-operator"],
   "env": {
     "test": {
       "plugins": ["@babel/plugin-transform-modules-commonjs"]

__tests__/functions.test.js

@@ -1,4 +1,4 @@
-import { curry, get, set, setIndex, toUpper } from '../src/functions'
+import { curry, get, isNil, set, setIndex, toUpper } from '../src/functions'
 
 const obj = { foo: 'bar' }
 const arr = [1, 2, 3]
@@ -15,6 +15,16 @@ describe('Function Operators', () => {
     expect(toUpper('yeah!')).toBe('YEAH!')
   })
 
+  test('isNil -> should work better than falsy values', () => {
+    expect(isNil(null)).toBe(true)
+    expect(isNil(undefined)).toBe(true)
+    expect(isNil(0)).toBe(false)
+    expect(isNil(-0)).toBe(false)
+    expect(isNil('')).toBe(false)
+    expect(isNil(NaN)).toBe(false)
+    expect(isNil(false)).toBe(false)
+  })
+
   test('get -> should retrieve the value of the property if it exists', () => {
     expect(get('foo')(obj)).toBe(obj.foo)
   })

package.json

@@ -36,7 +36,6 @@
     "@babel/core": "^7.11.6",
     "@babel/eslint-parser": "^7.11.5",
     "@babel/eslint-plugin": "^7.11.5",
-    "@babel/plugin-proposal-nullish-coalescing-operator": "^7.10.4",
     "@babel/plugin-transform-modules-commonjs": "^7.10.4",
     "@commitlint/cli": "latest",
     "@commitlint/config-conventional": "latest",

src/Lens.js

@@ -1,5 +1,5 @@
 import { fold } from './Fold'
-import { curry, get, set, setIndex } from './functions'
+import { curry, get, isNil, set, setIndex } from './functions'
 import { getter } from './Getter'
 import { isNotFound, notFound } from './notFound'
 import { optional } from './Optional'
@@ -68,7 +68,7 @@ export const mustBePresent = key => lens(get(key), set(key))
 // alter : String → Lens (Maybe s) (Maybe a)
 export const alter = key =>
   lens(
-    obj => (isNotFound(obj) ? notFound : obj[key] ?? notFound),
+    obj => (isNotFound(obj) || isNil(obj[key]) ? notFound : obj[key]),
     (val, obj) => {
       if (isNotFound(val)) {
         if (typeof obj === 'object') {

src/Optional.js

@@ -1,6 +1,6 @@
 import { OpticCreationError } from './errors'
 import { fold } from './Fold'
-import { curry, setIndex } from './functions'
+import { curry, isNil, setIndex } from './functions'
 import { isNotFound, notFound, notFoundToList } from './notFound'
 import { partialGetter } from './PartialGetter'
 import { setter } from './Setter'
@@ -56,14 +56,14 @@ export const optional = curry((preview, set) => new Optional(preview, set))
 // optionalProp : String → Optional s a
 export const optionalProp = key =>
   optional(
-    obj => obj[key] ?? notFound,
+    obj => (isNil(obj[key]) ? notFound : obj[key]),
     (val, obj) => (obj[key] ? { ...obj, [key]: val } : obj),
   )
 
 // optionalIx : Number → Optional s a
 export const optionalIx = index =>
   optional(
-    obj => obj[index] ?? notFound,
+    obj => (isNil(obj[index]) ? notFound : obj[index]),
     (val, obj) => (obj[index] ? setIndex(index, val, obj) : obj),
   )
 

src/functions.js

@@ -23,3 +23,5 @@ export const setIndex = curry((index, val, array) => array.map((v, i) => (i == i
 
 // toUpper : String -> String
 export const toUpper = str => str.toUpperCase()
+
+export const isNil = x => x === null || x === undefined