using prototype property

section4/script.js

@@ -12,11 +12,12 @@ var Person = function(name, yearOfBirth, job) {
   this.name = name;
   this.yearOfBirth = yearOfBirth;
   this.job = job;
-  this.calculateAge = function() {
-      console.log(2019 - this.yearOfBirth);
-  }
 };
 
+Person.prototype.calculateAge = function() { 
+    console.log(2019 - this.yearOfBirth);
+}
+
 var mike = new Person("mike", 1991, "developer");
 console.log(mike);
 mike.calculateAge();