how to use for in javascript for object code example

Example 1: how to create object js

function person(fname, lname, age, eyecolor){
  this.firstname = fname;
  this.lastname = lname;
  this.age = age;
  this.eyecolor = eyecolor;
}

myFather = new person("John", "Doe", 50, "blue");
document.write(myFather.firstname + " is " + myFather.age + " years old.");

Example 2: objects javascript

function Dog() {
  this.name = "Bailey"; 
  this.colour = "Golden"; 
  this.breed = "Golden Retriever";
  this.age = 8;
}