Merge pull request #60 from khusbuchandra/develop

Issue #45 : Add isNegativeInteger function

Author: jhowardjr

index.js

@@ -25,4 +25,5 @@ module.exports = Object.assign(
   require('./lib/sampleVariance.js'),
   require('./lib/isPositiveInteger.js'),
   require('./lib/isDecimal.js'),
+  require('./lib/isNegativeInteger.js'),
 );

lib/isNegativeInteger.js

@@ -0,0 +1,16 @@
+exports.isNegativeInteger = (...params) => {
+  for (const param of params) {
+    // Checks the type to be Number
+    if (Object.prototype.toString.call(param) !== '[object Number]' ||
+            // Is it an integer?
+            param % 1 !== 0 ||
+              // Is it positive?
+              param >= 0 ||
+              // maximum safe integer check
+              // / / https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER
+              param < Number.MIN_SAFE_INTEGER) {
+      return false;
+    }
+  }
+  return true;
+};

spec/isNegativeIntegerSpec.js

@@ -0,0 +1,29 @@
+const { isNegativeInteger } = require('../lib/isNegativeInteger');
+
+const MAX_SAFE_INTEGER = 9007199254740991;
+describe('IsNegativeInteger', () => {
+  it('should return false for positive integers or 0', () => {
+    expect(isNegativeInteger(2, 4, 200)).toBe(false);
+    expect(isNegativeInteger(MAX_SAFE_INTEGER, 4, 200)).toBe(false);
+    expect(isNegativeInteger(0, 98, 225, 56)).toBe(false);
+  });
+
+  it('should return true for negative numbers', () => {
+    expect(isNegativeInteger(-3, -4, -200)).toBe(true);
+    expect(isNegativeInteger(-34, -98, -225, -56)).toBe(true);
+  });
+
+  it('should return false for floats', () => {
+    expect(isNegativeInteger(2.6, 4.9, 23.67)).toBe(false);
+    expect(isNegativeInteger(2, 4, 23.67)).toBe(false);
+    expect(isNegativeInteger(-10.2, -4.6, -200.4)).toBe(false);
+    expect(isNegativeInteger(-32.7, 98, 225, 56)).toBe(false);
+  });
+
+  it('should return false for other values', () => {
+    expect(isNegativeInteger({})).toBe(false);
+    expect(isNegativeInteger(2, [])).toBe(false);
+    expect(isNegativeInteger(1, 'S')).toBe(false);
+    expect(isNegativeInteger(MAX_SAFE_INTEGER + 1)).toBe(false);
+  });
+});