Dean Edwards 写的强大的forEach

http://dean.edwards.name/

主要代码：

// array-like enumeration
if (!Array.forEach) { // mozilla already supports this
    Array.forEach = function(array, block, context) {
        for (var i = 0; i < array.length; i++) {
            block.call(context, array[i], i, array);
        }
    };
}

// generic enumeration
Function.prototype.forEach = function(object, block, context) {
    for (var key in object) {
        if (typeof this.prototype[key] == "undefined") {
            block.call(context, object[key], key, object);
        }
    }
};

// character enumeration
String.forEach = function(string, block, context) {
    Array.forEach(string.split(""), function(chr, index) {
        block.call(context, chr, index, string);
    });
};

// globally resolve forEach enumeration
var forEach = function(object, block, context) {
    if (object) {
        var resolve = Object; // default
        if (object instanceof Function) {
            // functions have a "length" property
            resolve = Function;
        } else if (object.forEach instanceof Function) {
            // the object implements a custom forEach method so use that
            object.forEach(block, context);
            return;
        } else if (typeof object == "string") {
            // the object is a string
            resolve = String;
        } else if (typeof object.length == "number") {
            // the object is array-like
            resolve = Array;
        }
        resolve.forEach(object, block, context);
    }
};

下面是测试代码：

function print(value, key, object, tag) {

          if (!tag) tag = "PRE";

        document.write("<" + tag + ">" + key + ": " + value + "</" + tag + ">");

      };

      

      print('"abc"', "forEach", null, "h3");

      forEach ("abc", print);

      

      print("[1, 2, 3]", "forEach", null, "h3");

      forEach ([1, 2, 3], print);

      

      print("{a:1, b:2, c:3}", "forEach", null, "h3");

      forEach ({a:1, b:2, c:3}, print);

      

      print("arguments(1, 2, 3)", "forEach", null, "h3");

      function test() {

          forEach (arguments, print);

      };

      test(1, 2, 3);

      

      print("fred", "forEach", null, "h3");

      function Person(name, age) {

          this.name = name || "";

          this.age = age || 0;

      };

      Person.prototype = new Person;

      Person.LATIN = "Homo Sapiens";

      var fred = new Person("Fred", 38);

      fred.language = "English";

      fred.wife = "Wilma";

      forEach (fred, print);

      

      print("fred", "Person.forEach", null, "h3");

      Person.forEach (fred, print);

      

      print("Person", "forEach", null, "h3");

      forEach (Person, print);