add isNegativeZero

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
+```

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

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();
+});