Determine if a number is an integer or not.

isInteger.js

var isInteger = (function(NEGATIVE_INFINITY, POSITIVE_INFINITY){
  return function(n){
    return typeof n === 'number' && // Are you even an number? Rules out non numeric types.
      n > NEGATIVE_INFINITY && // n larger than negative infinity? Rules out NaN and negative infinity.
      n < POSITIVE_INFINITY &&  // n smaller than positive infinity? Rules out NaN and positive infinity.
      !(n % 1); // n has a remainder of 0 when calculating modulo 1? Rules out floating points.
  };
}(-1/0, 1/0)); // just making sure we're getting negative and positive infinity

console.assert(isInteger(false) === false, 'booleans are not integers')
console.assert(isInteger(function(){}) === false, 'functions are not integers')
console.assert(isInteger(/1/) === false, 'regexps are not integers')
console.assert(isInteger([1]) === false, 'arrays are not integers')
console.assert(isInteger(Object(1)) === false, 'objects are not integers')
console.assert(isInteger('1') === false, 'strings are not integers')
console.assert(isInteger(Number.POSITIVE_INFINITY) === false, 'Infinity is not an integer')
console.assert(isInteger(Number.NEGATIVE_INFINITY) === false, '-Infinity is not an integer')
console.assert(isInteger(NaN) === false, 'NaN is not an integer')
console.assert(isInteger(1.1) === false, 'Floating points are not integers')
console.assert(isInteger(1) === true, '1 is an integer')
console.assert(isInteger(0) === true, '0 is an integer')
console.assert(isInteger(-0) === true, '-0 is an integer')
console.assert(isInteger(-1) === true, '-1 is an integer')
console.log('Everything is in working order.');