Adding isPositiveInteger function

Added isPositiveInteger function to check for positive integers not more than max safe integer. Added spec for the same.

Author: khusbuchandra

index.js

@@ -20,5 +20,6 @@ module.exports = Object.assign(
   require('./lib/populationStandardDeviation.js'),
   require('./lib/populationVariance.js'),
   require('./lib/sampleStandardDeviation.js'),
-  require('./lib/sampleVariance.js')
+  require('./lib/sampleVariance.js'),
+  require('./lib/isPositiveInteger.js')
 );

lib/isPositiveInteger.js

@@ -0,0 +1,18 @@
+
+exports.isPositiveInteger = (...params) => {
+    for (const param of params) {     
+       // Checks the type to be Number
+        if( params.some(param => typeof param !== '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.MAX_SAFE_INTEGER)
+            {
+                return false;
+            }
+        }
+    return true;
+  };

spec/isPositiveIntegerSpec.js

@@ -0,0 +1,32 @@
+const { isPositiveInteger } = require('../lib/isPositiveInteger');
+const MAX_SAFE_INTEGER =  9007199254740991;
+describe('IsPositiveInteger', () => {
+  it('should return true for positive integers', () => {
+    
+    expect(isPositiveInteger(2, 4, 200)).toBe(true)
+    expect(isPositiveInteger(MAX_SAFE_INTEGER, 4, 200)).toBe(true)
+    expect(isPositiveInteger(34,98,225,56)).toBe(true)
+  });
+
+  it('should return false for negative numbers or 0', () => {
+    
+    expect(isPositiveInteger(0, 4, 200)).toBe(false)
+    expect(isPositiveInteger(-3, -4, -200)).toBe(false)
+    expect(isPositiveInteger(34,-98,225,56)).toBe(false)
+  });
+
+  it('should return false for floats', () => {    
+    expect(isPositiveInteger(2.6, 4.9, 23.67)).toBe(false)
+    expect(isPositiveInteger(2, 4, 23.67)).toBe(false)
+    expect(isPositiveInteger(-10.2, -4.6, -200.4)).toBe(false)
+    expect(isPositiveInteger(-32.7,98,225,56)).toBe(false)
+  });
+
+  it('should return false for other values', () => {    
+    expect(isPositiveInteger({})).toBe(false)
+    expect(isPositiveInteger(2,[])).toBe(false)
+    expect(isPositiveInteger(1,'S')).toBe(false)
+    expect(isPositiveInteger(MAX_SAFE_INTEGER + 1)).toBe(false)
+
+  });
+});