javascript forEach函数实现代码

function forEach(object, block, context, fn) { 
if (object == null) return; 
if (!fn) { 
if (typeof object == "function" && object.call) { 
//遍历普通对象 
fn = Function; 
} else if (typeof object.forEach == "function" && object.forEach != arguments.callee) { 
//如果目标已经实现了forEach方法，则使用它自己的forEach方法（如标准游览器的Array对象） 
object.forEach(block, context); 
return; 
} else if (typeof object.length == "number") { 
// 如果是类数组对象或IE的数组对象 
_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) { 
// 这里的fn恒为Function 
for (var key in object) { 
//只遍历本地属性 
if (object.hasOwnProperty(key)) { 
//相当于 block(object[key], key) 
block.call(context, object[key], key, object); 
} 
} 
};

原作者的一些例子（我***扒过来了！）：

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 forEach(object, block, context, fn) {
if (object == null) return;
if (!fn) {
if (typeof object == "function" && object.call) {
//遍历普通对象
fn = Function;
} else if (typeof object.forEach == "function" && object.forEach != arguments.callee) {
//如果目标已经实现了forEach方法，则使用它自己的forEach方法（如标准游览器的Array对象）
object.forEach(block, context);
return;
} else if (typeof object.length == "number") {
// 如果是类数组对象或IE的数组对象
_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")
array = array.split("");
for (;i < length; i++) {
block.call(context, array[i], i, array);
}
};
_Function_forEach = function(fn, object, block, context) {
// 这里的fn恒为Function
for (var key in object) {
//只遍历本地属性
if (object.hasOwnProperty(key)) {
//相当于 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) }); [Ctrl+A 全选 注:如需引入外部Js需刷新才能执行]

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

function forEach(object, block, context, fn) {
if (object == null) return;
if (!fn) {
if (typeof object == "function" && object.call) {
//遍历普通对象
fn = Function;
} else if (typeof object.forEach == "function" && object.forEach != arguments.callee) {
//如果目标已经实现了forEach方法，则使用它自己的forEach方法（如标准游览器的Array对象）
object.forEach(block, context);
return;
} else if (typeof object.length == "number") {
// 如果是类数组对象或IE的数组对象
_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")
array = array.split("");
for (;i < length; i++) {
block.call(context, array[i], i, array);
}
};
_Function_forEach = function(fn, object, block, context) {
// 这里的fn恒为Function
for (var key in object) {
//只遍历本地属性
if (object.hasOwnProperty(key)) {
//相当于 block(object[key], key)
block.call(context, object[key], key, object);
}
}
};

function print(el,index){
alert(index+" : "+el)
}
function Person(name, age) {
this.name = name || "";
this.age = age || 0;
};
Person.prototype = new Person;

var fred = new Person("Fred", 38);
fred.language = "English";//极晚绑定
fred.wife = "Wilma";//极晚绑定
forEach(fred,print)
[Ctrl+A 全选 注:如需引入外部Js需刷新才能执行]