SOURCE

// 为null的对象，类型为 object,
// 但是值为 undefined
var obj = null;
console.log("type of obj = " + typeof obj);
console.log("obj == undefined ? " + (obj == undefined));
console.log("obj ===  undefined ? " + (obj === undefined));

// 使用console实现换行
console.log("\n \n \n");


var foo;
console.log("foo = " + foo);
console.log("!foo = " + !foo);
console.log("!!foo = " + !!foo);

// 使用console实现换行
console.log("\n \n \n");

var myNaN = 1;
console.log("myNaN = " + myNaN);
console.log("myNaN === myNaN ? " + (myNaN === myNaN) );
console.log("myNaN !== myNaN ? " + (myNaN !== myNaN) );

function isNaN (param) {
  console.log("param is NaN ? " + (!!(param !== param) ) );
}

isNaN(1);