Prototypes in Javascript

First class functions?

• Create new functions from preexisting functions at run-time
• Store functions in collections
• Use functions as arguments to other functions
• Use functions as return values of other functions

A language supports first class functions if:

What is an Object

//this is an object
var myObject = {};

//you can add properties(values) and methods(functions) to an object

myObject.name = 'Sam Object';

myObject.whatIsMyName = function() {
    return this.name;
}

//That's it.

What's wrong with this Object?

I can't reuse it or make multiple copies of it.

KWOW THESE WORDS

• CLASS/FUNCTION
• OBJECT
• INSTANCE

...AND WHY THEY ARE DIFFERENT

ALSO IMPORTANT

• INHERITANCE
• CONSTRUCTOR
• CONTEXT

http://stackoverflow.com/questions/17525450/object-vs-class-vs-function

What Are Prototypes

• Prototypes are JUST Functions
  • new keyword is what depicts the difference between JUST a function and a constructor
• Prototypes are SINGULAR
  • Prototype functions can have different CONTEXT but are same instance of function. This has a small memory footprint.
• EVERY object has a prototype
• Every object inherits from Object..and it's prototype
  • This is called prototypical inheritance​

Things to Know about Prototypes

• Adding a new prototype to a class will affect ALL instances of the class even if they are already created.
• Adding a new function to a class will affect ONLY that SINGLE instance of a class.
• Instance members of the same name will OVERRIDE the prototype member of the same name. This happens because of order. Prototype happens first. Constructor second.
• Prototype is a property of the constructor

The prototype Inheritance Chain

• All objects that inherit from another object receive all prototype properties of all objects up the prototype chain
• Adding to a prototype anywhere in the prototype chain will add property all the way up the chain.
• hasOwnProperty() will tell you if the method is defined on the current object or inherited.
• Inheritance ONLY inherits prototypes not properties.
• Example: forEach example to support legacy browsers

if (!Array.prototype.forEach) {
 Array.prototype.forEach = function(callback, context) {
     for (var i = 0; i < this.length; i++) {
         callback.call(context || null, this[i], i, this);
     }
 };
}

Things to know

• NEVER extend the Object prototype.
• Prototype definitions are not hoisted because of assignment
• __proto__ : now forget about it.
• Since a constructor is just a function you can call it like a method without new.
  • Name your classes upper case as a visual signal.
  • This will make the context of the object the global scope.
  • Example of human proofing:

function User(first, last) {
 if (!(this instanceof arguments.callee)) {
     return new User(first,last);
 }
 this.name = first + " " + last;
}