console.log('Math.sqrt(-2)', Math.sqrt(-2));

console.log('Math.log(-1)', Math.log(-1));

console.log('0/0', 0/0);

console.log('parseFloat("foo")', parseFloat('foo'));

​

console.log('typeof NaN is ' + typeof NaN);

​

var x = Math.sqrt(-2);

var y = Math.log(-1);

console.log('Math.sqrt(-2) == Math.log(-1)', x == y);

​

var x = Math.sqrt(-2);

var y = Math.log(-1);

console.log('Math.sqrt(-2) === Math.log(-1)', x === y);

​

var x = Math.sqrt(-2);

var y = Math.sqrt(-2);

console.log('Math.sqrt(-2) === Math.sqrt(-2)', x === y);

​

var x = Math.sqrt(-2);

console.log('x = Math.sqrt(-2); x === x', x === x);

​

​

console.log('NaN === NaN', NaN === NaN);

​

console.log('isNaN(NaN)', isNaN(NaN));

console.log('isNaN(Math.sqrt(-2))', isNaN(Math.sqrt(-2)));

​

console.log('isNaN(\'hello\')', isNaN('hello'));

console.log('isNaN([\'x\'])', isNaN(['x']));

console.log('isNaN({})', isNaN({}));

​

var My = {

  isNaN: function (x) { return x !== x; }

}

​

My.isNaN = function(x) { return typeof x === 'number' && isNaN(x)};

​

console.log('My.isNaN(NaN)', My.isNaN(NaN));

console.log('My.isNaN(Math.sqrt(-2))', My.isNaN(Math.sqrt(-2)));

console.log('My.isNaN(\'hello\')', My.isNaN('hello'));

console.log('My.isNaN([\'x\'])', My.isNaN(['x']));

console.log('My.isNaN({})', My.isNaN({}));

​

​

if (Number.isNaN) {

  console.log('Number.isNaN(NaN)', Number.isNaN(NaN));

  console.log('Number.isNaN(Math.sqrt(-2))', Number.isNaN(Math.sqrt(-2)));

  console.log('Number.isNaN(\'hello\')', Number.isNaN('hello'));

  console.log('Number.isNaN([\'x\'])', Number.isNaN(['x']));

  console.log('Number.isNaN({})', Number.isNaN({}));

}