fix: correctly count undefined and null args

upgrade dev dependencies

index.js

@@ -3,6 +3,6 @@ module.exports = function xor(...args) {
     return false;
   }
 
-  const truthyCount = args.reduce((result, val) => result + !!val);
+  const truthyCount = args.reduce((result, val) => result + !!val, 0);
   return truthyCount === 1;
 };

index.test.js

@@ -1,11 +1,17 @@
 const xor = require('.');
 
 test('not enough arguments', () => {
+  expect(xor()).toBe(false);
+  expect(xor(undefined)).toBe(false);
+  expect(xor(null)).toBe(false);
   expect(xor(true)).toBe(false);
   expect(xor(false)).toBe(false);
 });
 
 test('2 args', () => {
+  expect(xor(undefined, undefined)).toBe(false);
+  expect(xor(undefined, true)).toBe(true);
+  expect(xor(null, true)).toBe(true);
   expect(xor(true, false)).toBe(true);
   expect(xor(false, true)).toBe(true);
   expect(xor(true, true)).toBe(false);
@@ -17,5 +23,7 @@ test('many arguments', () => {
   expect(xor(true, true, true)).toBe(false);
   expect(xor(true, true, false)).toBe(false);
   expect(xor(false, false, false)).toBe(false);
+  expect(xor(undefined, true, false, false)).toBe(true);
+  expect(xor(undefined, null, false, false)).toBe(false);
   expect(xor(false, false, false, false, false, true)).toBe(true);
 });

package.json

@@ -13,16 +13,20 @@
     "node": ">= 4.9"
   },
   "scripts": {
-    "precommit": "pretty-quick --staged",
     "test": "jest"
   },
   "devDependencies": {
-    "husky": "^0.14.3",
-    "jest": "^24.7.1",
-    "prettier": "^1.17.0",
-    "pretty-quick": "^1.10.0"
+    "husky": "^3.0.3",
+    "jest": "^24.8.0",
+    "prettier": "^1.18.2",
+    "pretty-quick": "^1.11.1"
   },
   "prettier": {
     "singleQuote": true
+  },
+  "husky": {
+    "hooks": {
+      "pre-commit": "pretty-quick --staged"
+    }
   }
 }