From b723a931b7198375fe37e717eeeb01f79168b0cc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Feje=C5=A1?= <ns.fejes.stefan@gmail.com>
Date: Mon, 12 Nov 2018 14:45:36 +0100
Subject: [PATCH] add isNegativeZero

---
 snippets/isNegativeZero.md  | 14 ++++++++++++++
 tag_database                |  1 +
 test/isNegativeZero.test.js | 15 +++++++++++++++
 3 files changed, 30 insertions(+)
 create mode 100644 snippets/isNegativeZero.md
 create mode 100644 test/isNegativeZero.test.js

diff --git a/snippets/isNegativeZero.md b/snippets/isNegativeZero.md
new file mode 100644
index 000000000..e4d4df5a0
--- /dev/null
+++ b/snippets/isNegativeZero.md
@@ -0,0 +1,14 @@
+### isNegativeZero
+
+Checks if the given value is a negative zero `-0`.
+
+Checks whether a passed value is equal to `0` and if one devided by the value equals `-Infinity`.
+
+```js
+const isNegativeZero = val => val === 0 && 1 / val === -Infinity;
+```
+
+```js
+isNegativeZero(-0); // true
+isNegativeZero(0); // false
+```
diff --git a/tag_database b/tag_database
index aaa61a47e..436fb8869 100644
--- a/tag_database
+++ b/tag_database
@@ -145,6 +145,7 @@ isEmpty:type,array,object,string,beginner
 isEven:math,beginner
 isFunction:type,function,beginner
 isLowerCase:string,utility,beginner
+isNegativeZero:math,utility,beginner
 isNil:type,beginner
 isNull:type,beginner
 isNumber:type,math,beginner
diff --git a/test/isNegativeZero.test.js b/test/isNegativeZero.test.js
new file mode 100644
index 000000000..963693a43
--- /dev/null
+++ b/test/isNegativeZero.test.js
@@ -0,0 +1,15 @@
+const expect = require('expect');
+const { isNegativeZero } = require('._30s.js');
+
+test('isNegativeZero is a Function', () => {
+  expect(isNegativeZero).toBeInstanceOf(Function);
+});
+test('0 is not a -0', () => {
+  expect(isNegativeZero(0)).toBeFalsy();
+});
+test('-0 is a negative zero', () => {
+  expect(isNegativeZero(-0)).toBeTruthy();
+});
+test('1 is not a negative zero', () => {
+  expect(isNegativeZero(1)).toBeFalsy();
+});