encapsulation chapter: javascript => DONE

Author: kariminf

book/encapsulation.tex

@@ -63,12 +63,26 @@ \subsection{Java}
 \subsection{Javascript} 
 
 All fields with the keyword \keyword{this} are public. 
-All  methods defined using the same keyword inside the constructor or using the prototype are public.
+All methods defined using the same keyword inside the constructor or using the prototype are public.
 
-%\lstinputlisting[linerange={1-1,5-5}, style=codeStyle]{../codes/javascript/person2.js}
-%
-%\lstinputlisting[linerange={1-1,15-15}, style=codeStyle]{../codes/javascript/person.js}
+\lstinputlisting[linerange={3-4,12-12,16-16,22-22}, style=codeStyle]{../codes/javascript/encapsulation/person.js}
+
+Which can be accessed anywhere
+
+\lstinputlisting[linerange={1-1,4-4,7-7,12-12}, style=codeStyle]{../codes/javascript/encapsulation/app.js}
 
+Actually, objects in Javascript can be updated by assigning them new fields and methods dynamically. 
+This gives you the power to upgrade existing prototypes (classes) and decorate objects without the need to create more classes.
+Also, as \nameword{uncle Ben} of \nameword{Spider-man} once said: ``\textit{With great power comes great responsibility}".
+
+\lstinputlisting[linerange={1-17}, style=codeStyle]{../codes/javascript/encapsulation/decorate.js}
+
+Here, we created two objects, but with different fields. 
+Then, we can create a function which print different fields of a Person. 
+Just a note: you have to verify that the member is not a function, since functions in Javascript are first class objects. 
+Which means: they are a type (\keyword{function}), they are instances of \keyword{Object} and they can be treated as any variable.
+
+\lstinputlisting[linerange={19-29}, style=codeStyle]{../codes/javascript/encapsulation/decorate.js}
 
 \subsection{Lua}
 
@@ -156,13 +170,15 @@ \subsection{Java}
 
 \lstinputlisting[language=Java, linerange={3-3,7-7,29-29,31-34}, style=codeStyle]{../codes/java/src/encapsulation/core/Person.java}
 
-
 \subsection{Javascript} 
 
-%\lstinputlisting[linerange={1-1,5-5}, style=codeStyle]{../codes/javascript/person2.js}
-
-%\lstinputlisting[linerange={1-1,15-15}, style=codeStyle]{../codes/javascript/person.js}
+There is no protected members in Javascript. 
+You can find some hacks on the web, but they can be expensive in term of memory and processing power.
+To emulate such mechanism, you have to know the caller object 
+If you insist on having protected and private members, some libraries can be helpful such as \nameword{mozart}\footnote{mozart: \url{https://github.com/philipwalton/mozart}}.
 
+% https://philipwalton.com/articles/implementing-private-and-protected-members-in-javascript/
+% https://philipwalton.com/articles/implementing-private-and-protected-members-in-javascript/
 
 \subsection{Lua}
 
@@ -269,9 +285,13 @@ \subsection{Java}
 
 \subsection{Javascript} 
 
-%\lstinputlisting[linerange={1-1,5-5}, style=codeStyle]{../codes/javascript/person2.js}
-%
-%\lstinputlisting[linerange={1-1,15-15}, style=codeStyle]{../codes/javascript/person.js}
+There is a convention to use underscore \keyword{\_} as a mean to signal a class member as private. 
+But the member still accessible as public. 
+Another way is to use closures (the combination of a function and the lexical environment within which that function was declared), by defining a field inside the constructor using the keyword \keyword{var} or \keyword{let}.
+But, any method using this variable must be defined inside the constructor.
+This means each time you create a new instance (object), a new function will be created for this object. 
+
+
 
 
 \subsection{Lua}

codes/javascript/encapsulation/app.js

@@ -0,0 +1,13 @@
+var Person = require("person.js");
+var Student = require("student.js");
+
+var p = new Person("Karim_p");
+var s = new Student("Karim_s");
+
+console.log(p.luckyNumber);
+console.log(p._name);
+console.log(p.num);//undefined
+console.log(p.t);
+
+p.info();
+s.info();

codes/javascript/encapsulation/decorate.js

@@ -0,0 +1,29 @@
+let Person = function(name) {
+  this.name = name;
+}
+
+function create(name, members) {
+  let p = new Person(name);
+  p = Object.assign(p, members);
+  return p;
+}
+
+let student = create ("Karim_s", {
+  year: 2
+});
+
+let teacher = create ("Karim_t", {
+  courses: ["C1", "C2"]
+});
+
+function info (person) {
+  console.log(person.name);
+  for(let member in person){
+    if (typeof member != "function") {
+      console.log(member, " = ", person[member]);
+    }
+  }
+}
+
+info(student);
+info(teacher);

codes/javascript/encapsulation/person.js

@@ -1,33 +1,22 @@
+module.exports = Person;
+
 function Person(name) {
   this.luckyNumber = 0;
   this._name = name;
   var num = Person.nbr;
   Person.nbr++;
 
   this.info1 = function(){
-    console.log("My name: ${this._name}");
     console.log("My number is: ${num}");
   }
 }
 
 Person.nbr = 0;
 
 Person.prototype.info = function(){
-	console.log("My name: " + this.name + ", My birth year: " + this.byear);
-}
-
-Person.population = function(){
-	return Person.nbr;
+  console.log("My name: ${this._name}");
+  this.info1();
+  console.log("I am a: " + t);
+  console.log("My lucky number is: " + luckyNumber);
+  console.log("--------------------------");
 }
-
-var p = new Person("Karim", 1986);
-var p2 = new Person("Karim+1", 1987);
-
-p.info();
-p2.info();
-var nbr = Person.population();
-
-console.log("The number of persons: " + nbr);
-p2 = null;
-nbr = Person.population();
-console.log("The number of persons: " + nbr);

codes/javascript/encapsulation/student.js

@@ -1,27 +1,14 @@
-function Person(name, byear) {
-  this.name = name;
-  this.byear = byear;
-  Person.nbr++;
-}
-
-Person.nbr = 0;
+var Person = require("person.js");
 
-Person.prototype.info = function(){
-	console.log("My name: " + this.name + ", My birth year: " + this.byear);
-}
+module.exports = Student;
 
-Person.population = function(){
-	return Person.nbr;
+function Student(name) {
+  Person.call(this, name);
+  this._name = name + "2";//can be accessed
+  console.log("Student => num = ", num, ", this.num = ", this.num);
+  this.t = "student";
+  luckyNumber = 1;
 }
 
-var p = new Person("Karim", 1986);
-var p2 = new Person("Karim+1", 1987);
-
-p.info();
-p2.info();
-var nbr = Person.population();
-
-console.log("The number of persons: " + nbr);
-p2 = null;
-nbr = Person.population();
-console.log("The number of persons: " + nbr);
+Student.prototype = Object.create(Person.prototype);
+Student.constructor = Student;