//1、 typeof
var a = 12;
typeof a// ---> \'number\'
typeof \'number\' // ---> \'string\'
typeof true // ----> \'boolean\'
typeof \'true\' // ---> \'string\'
typeof null // ---> \'object\'
typeof undefined // ---> \'undefined\'
typeof ({}) // ---> \'object\'
typeof ([]) // ---> \'object\'
//2、constructor
var str = \'www\';
console.log(str.constructor.toString());
console.log(a.constructor.toString());
console.log(({}).constructor.toString());
console.log(([]).constructor.toString());
// console.log(null.constructor);
//3、 instanceof 查看对象
var obj = {};
var ary = [];
console.log(obj instanceof Array); // false
console.log(ary instanceof Array); // true
console.log(obj instanceof Object);// true
console.log(ary instanceof Object);// true
//4、Object.prototype.toString.call(xxx);
console.log(Object.prototype.toString.call([]));
console.log(Object.prototype.toString.call({}));
console.log(Object.prototype.toString.call(/\d/));
console.log(Object.prototype.toString.call(12));
console.log(Object.prototype.toString.call(\'www\'));
console.log(Object.prototype.toString.call(true));