function forEach(object, block, context, fn) {
if (object == null) return;
if (!fn) {
if (typeof object == "function" && object.call) {
//遍歷普通對象
fn = Function;
} else if (typeof object.forEach == "function" && object.forEach != arguments.callee) {
//如果目標(biāo)已經(jīng)實現(xiàn)了forEach方法，則使用它自己的forEach方法（如標(biāo)準(zhǔn)游覽器的Array對象）
object.forEach(block, context);
return;
} else if (typeof object.length == "number") {
// 如果是類數(shù)組對象或IE的數(shù)組對象
_Array_forEach(object, block, context);
return;
}
}
_Function_forEach(fn || Object, object, block, context);
};
function _Array_forEach(array, block, context) {
if (array == null) return;
var i = 0,length = array.length;
if (typeof array == "string") {
for (; i < length; i++) {
block.call(context, array.charAt(i), i, array);
}
}else{
for (;i < length; i++) {
block.call(context, array[i], i, array);
}
}
};
_Function_forEach = function(fn, object, block, context) {
// 這里的fn恒為Function
for (var key in object) {
//只遍歷本地屬性
if (object.hasOwnProperty(key)) {
//相當(dāng)于 block(object[key], key)
block.call(context, object[key], key, object);
}
}
};

function print(el,index){
alert(index+" : "+el)
}
forEach ([1, 2, 3], print);
forEach ({a: "aa", b: "bb",c: "cc"}, print);
forEach ("司徒正美", print);
forEach(document.styleSheets,function(el){
if(el.href) alert(el.href)
});

function Person(name, age) {
this.name = name || "";
this.age = age || 0;
};
Person.prototype = new Person;
var fred = new Person("Fred", 38);
fred.language = "English";//極晚綁定
fred.wife = "Wilma";//極晚綁定
forEach(fred,print)