What's the difference? => A lot.
I think, the this version is used to enable encapsulation, i.e. data hiding.
It helps to manipulate private variables.
Let us look at the following example:
var AdultPerson = function() {
var age;
this.setAge = function(val) {
// some housekeeping
age = val >= 18 && val;
};
this.getAge = function() {
return age;
};
this.isValid = function() {
return !!age;
};
};
Now, the prototype structure can be applied as following:
Different adults have different ages, but all of the adults get the same rights.
So, we add it using prototype, rather than this.
AdultPerson.prototype.getRights = function() {
// Should be valid
return this.isValid() && ['Booze', 'Drive'];
};
Lets look at the implementation now.
var p1 = new AdultPerson;
p1.setAge(12); // ( age = false )
console.log(p1.getRights()); // false ( Kid alert! )
p1.setAge(19); // ( age = 19 )
console.log(p1.getRights()); // ['Booze', 'Drive'] ( Welcome AdultPerson )
var p2 = new AdultPerson;
p2.setAge(45);
console.log(p2.getRights()); // The same getRights() method, *** not a new copy of it ***
Hope this helps.