var objStr = new Object('');
alert(objStr.constructor);//String
alert(isPlainObject(objStr));//false
var objNum = new Object(3);
alert(objNum.constructor);//Number
alert(isPlainObject(objNum));//false
function Person(){}
var person = new Person();
alert(isPlainObject(person));//false
var obj01 = new Object();
obj01.name = '笨蛋的座右銘';
alert(isPlainObject(obj01));//true
alert(isPlainObject({name:'笨蛋的座右銘'}));//true

var toString = Object.prototype.toString,
hasOwnProperty = Object.prototype.hasOwnProperty;
function isPlainObject( obj ) {
// Must be an Object.
// Because of IE, we also have to check the presence of the constructor property.
//Make sure that DOM nodes and window objects don't pass through, as well
//windows objects:toString.call(window):IE [object Object] FF [object Window] chrome [window global] safari [object DOMWindow]
//DOM nodes:toString.call(#div01):IE [object Object] FF [object Window] chrome [object global] safari [object DOMWindow]
//結(jié)論：obj.nodeType || obj.setInterval主要是針對(duì)于IE瀏覽器進(jìn)行判斷
//注：history,location,navigator,screen的setInterval為undefined
if ( !obj || toString.call(obj) !== "[object Object]" || obj.nodeType || obj.setInterval ) {
return false;
}
// Not own constructor property must be Object
// 除去自定義對(duì)象和內(nèi)置對(duì)象的判斷,如function Person(){} var p = new Person();String,Number
if ( obj.constructor //有constructor屬性
&& !hasOwnProperty.call(obj, "constructor") //并且constructor這個(gè)屬性必須是在原型鏈中進(jìn)行定義的
&& !hasOwnProperty.call(obj.constructor.prototype, "isPrototypeOf")//并且原型中有isPrototypeOf方法，一般只有Object的原型中才有這個(gè)方法
) {
return false;
}
// Own properties are enumerated firstly, so to speed up,
// if last one is own, then all properties are own.
//針對(duì)于復(fù)雜類(lèi)結(jié)構(gòu)，如有繼承...
/*
//一個(gè)簡(jiǎn)單的測(cè)試
function Animal(name){
}
function Person(name,age){
Animal.call(this,name);
this.age =age;
}
var p = new Person('jxl',20);
for(key in p){
alert(hasOwnProperty.call( p, key ))//true , false
}
*/
var key;
for ( key in obj ) {}
return key === undefined || hasOwnProperty.call( obj, key );
}

function isPlainObject(obj){
if(obj&&Object.prototype.toString.call(obj)==="[object Object]"&&obj.constructor===Object &&!hasOwnProperty.call(obj, "constructor")){
var key;
for ( key in obj ) {}
return key === undefined || hasOwnProperty.call( obj, key );
}
return false;
}

function m(){};
m.prototype.constructor=Object; //必殺
obj=new m;
alert(isPlainObject(obj)); //true

function m(){};
m.prototype = {};
obj=new m;
alert(isPlainObject(obj)); //true

function Person(){};
Person.prototype.constructor=Object;
var person=new Person;