类型判断

基本数据类型用typeof

var a = "test";
console.log(typeof(a));     // string

复合类型用instanceof和constructor

var b = new Date();
console.log(b instanceof Date);    // true

console.log(b.constructor === Date);  // true

通用方式 prototype

var a = "test";
var b = new Date();
console.log(Object.prototype.toString.call(a) === '[object String]');  // true
console.log(Object.prototype.toString.call(b) === '[object Date]');  // true