2. IS JAVASCRIPT OBJECT-ORIENTED? Contains objects Data Methods Doesn’t have classes Does have constructors Does have prototype functions Doesn’t provide information hiding??? No private members “per se” Can closures be used???

3. DOUGLAS CROCKFORD’S METHOD // Person class – example of access to private data members via functions function Person(firstName, lastName) { // Define a `getName()` function for combining the private name variables. this.getName = function() { return firstName + " " + lastName; }; // Define a `setLastName()` function to update the private last name variable. this.setLastName = function(newLastName) { lastName = newLastName; return this; }; } // Sets age for object, but publicly Person.prototype.setAge = function(age) { this.age = age; }; // Getter for the public `age` property Person.prototype.getAge = function() { return this.age; };

4. DOWNFALL OF CROCKFORD’S METHOD All instances of the Person pseudo-class have unique private member accessor methods. var a = new Person("John", "Resig"), b = new Person("Douglas", "Crockford"); alert(a.getName == b.getName); // false alert(a.getAge == b.getAge); // true Prototype functions don’t have direct access to the private members. Person.prototype.getFirstName = function() { return this.getName().replace(/.*? /g, ""); }; No direct access to the private members. If first name has a space in it, this will not work correctly.

5. PRIVILEGED PROTOTYPE FUNCTIONS Prototype functions are good — no unnecessary duplication Prototype functions have access to any variables in their ancestral function scopes Let’s use a closure to solve our dilemma

6. PRIVILEGED PROTOTYPE FUNCTIONS (function(key) { // Define Person in global scope Person = function(firstName, lastName) { // Store private members in one object. var privateVars = { firstName : firstName, lastName : lastName }; // Define a getter function that will only return private members // for privileged functions. this._ = function(aKey) { return aKey === key && privateVars; }; /* PROTOTYPE FUNCTIONS DEFINED ON NEXT SLIDE */ })({});

7. PRIVILEGED PROTOTYPE FUNCTIONS (function(key) { /*...CODE IN CLOSURE FROM PREVIOUS SLIDE... */ // Define a getter for the full name. Person.prototype.getName = function() { var _ = this._(key); return _.firstName + " " + _.lastName; }; // Define a setter for the last name. Person.prototype.setLastName = function(newLastName) { this._(key).lastName = newLastName; return this; }; // Define a getter for the first name. Person.prototype.getFirstName = function() { return this._(key).firstName; }; })({});

8. PROS & CONS Pros Create prototype functions that now have access to private variables. Eliminate duplication of getters and setters for each instance. Using a closure to prevent access from outside code. Cons A function call to access private members. Still have one function that is being duplicated for each instance. Overwriting the `_` (underscore) function will render the object useless. If the closure code is changed, the private members can become public.

9. FINAL NOTES The pros outweigh the cons. The `_` (underscore) function is really lightweight. Developers rarely overwrite an object’s `_` (underscore) property. Being able to change the code will always be a con of client-side JS code. Currently in use jPaq Color object implementation of a JS Hashtable classHashtable JavaScript is not necessarily object-oriented, but due to its unique capabilities, it doesn’t need to be.