forEach in javascript the right way

gistfile1.js

/*
    forEach, version 1.0
    Copyright 2006, Dean Edwards
    License: http://www.opensource.org/licenses/mit-license.php
*/

// 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);
  }
};​