类型运算符

console.log(typeof Math.PI); // number
console.log(typeof NaN); // number
console.log(typeof Infinity); // number
console.log(typeof true); // boolean
console.log(typeof undefined); // undefined
console.log(typeof function() {}); // function
console.log(typeof Array.isArray); // function
console.log(typeof Object());// object
console.log(typeof new Object()); // object
console.log(typeof {}); // object
console.log(typeof Array()); // object
console.log(typeof new Array()); // object
console.log(typeof []); // object
console.log(typeof null); // object
console.log(typeof String('test')); // string
console.log(typeof Number(123)); // number
console.log(typeof new Number(123)); // object
console.log(typeof Date()); // string
console.log(typeof new Date()); // object