how to access object from properties in javascript code example

Example 1: creating an object javascript

let obj = {
// fields
  name:"value",
  num: 123,
//methods
  foo: function(){}
  
}

Example 2: 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.");