Same property name for different obj

Question

If I have a few objects with the same property "age" then how JS know which I mean here???:

function yearBorn(){
return 2016-this.age;
}

Answer 1

"this" represents your actual object. This code is most likely inside a function in which you iterate through multiple objects, I guess. Or maybe it's in the object definition, in which case it will take the "age" of the object you will then create.

Answer 2

I try and what I know:
- If a few objects have same property "age" and function "yearBorn()", then calling that function works for all these objects.
- If first object has property and function/method and second one has only property, then calling function works only for first object.
Excellent!

You can try this code to test:
function person(name,age){
this.name=name;
this.age=age;
this.yearOfBirth=yearBorn;
}

function monster(name,age){
this.name=name;
this.age=age;
// this.yearOfBirth=yearBorn;
}

function yearBorn(){
return 2016-this.age;
}

var p1 = new person("Hero",33);

var m1 = new monster("ArchLich",500);

yearBorn();

document.write(p1.name," is ",p1.age," y.o.<br/> He was born in ",p1.yearOfBirth()," year.<br/>");
document.write(m1.name," is ",m1.age," y.o.<br/>");
/*document.write(m1.name," is ",m1.age," y.o.<br/> He was born in ",m1.yearOfBirth()," year.<br/>");*/