JavaScript and Object Oriented Programming (OOP)

JavaScript and Object Oriented Programming (OOP)
An object constructor is merely a regular JavaScript function, so it's just as robust (ie: define parameters, call other functions etc). The difference between the two is that a constructor function is called via the new operator

function cat(name) {
    this.name = name;
    this.talk = function() {
        alert( this.name + " say meeow!" )
    }
} 

cat1 = new cat("felix")
cat1.talk() //alerts "felix says meeow!"

cat2 = new cat("ginger")
cat2.talk() //alerts "ginger says meeow!"

We use it when we would like an object to inherit a method after it has been defined. Think of prototyping mentally as "attaching" a method to an object after it's been defined, in which all object instances then instantly share.

cat.prototype.changeName = function(name) {
 this.name = name;
}

firstCat = new cat("pursur")
firstCat.changeName("Bill")
firstCat.talk() //alerts "Bill says meeow!"

JavaScript supports prototype inheritance instead of class based. It's possible for inheritance to happen other ways, however.

function superClass() {
  this.supertest = superTest; //attach method superTest
}

function subClass() {
  this.inheritFrom = superClass;
  this.inheritFrom();
  this.subtest = subTest; //attach method subTest
}

function superTest() {
  return "superTest";
}
  
function subTest() {
  return "subTest";
}


 var newClass = new subClass();

  alert(newClass.subtest()); // yields "subTest"
  alert(newClass.supertest()); // yields "superTest"