A Simple Example About Privileged Methods in JavaScript
private, privileged and public.
privileged methods? To understand that, we should have a short review of how we implement public and private methods in JavaScript first.
access specifiers like public, protected and
private. Lack of these features make the creation of private and public methods less clear than it should be.
public method in JavaScript, we make use of the .prototype property of the constructor function. For example:
function FootballPlayer(){}; // declare a function
FootballPlayer.prototype.kick = function(){ alert("kick!"); }; // create a public method kick in .prototype
var Messi = new FootballPlayer();
Messi.kick();
From my previous article, you have learnt that FootballPlayer.prototype is an object that is built automatically when the function is created. Object constructed with the FootballPlayer, Messi, search through his
__proto__ chain when we tell him to kick. Obviously FootballPlayer.prototype is on the chain so Messi knows how to kick. All objects created by the
constructor function share the same FootballPlayer.prototype so they all can invoke the
public method kick!
constructor using the keyword var:
function man() {
var wealth;
var bath = function(){};
function kiss(){}
}
In this case, none of wealth, bath or kiss are accessible outsite the function man. Even man's
public methods cannot access them.
privileged methods can access the private members due to the existence of
closures. They are very useful as they can act as a bridge between the outsite world and the inner status of the object.
var func = function(a,b) {
this.a = a;
this.getB = function(){return b}; // a privileged method
this.setB = function(n){b=n;}; // another privileged method
var b = b;
};
func.prototype.getB2 = function(){return b*2}; // public method var obj = new func(1,2);
alert(obj.getB()); // privileged method can access private b
alert(obj.getB2()); // error: public method cannot access private b
obj.setB(11);
alert(obj.getB());
So actually we can create privileged methods easily by using the keyword
this!
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