get and set method in JS

Types of Properties
There are two different types of properties: data properties and accessor
properties. Data properties contain a value, like the name property from earlier examples in this chapter.
The default behavior of the [[Put]] method
is to create a data property, and every example up to this point in the
chapter has used data properties. Accessor properties don’t contain a value
but instead define a function to call when the property is read (called
a getter), and a function to call when the property is written to (called a
setter). Accessor properties only require either a getter or a setter, though
they can have both.
There is a special syntax to define an accessor property using an
object literal:
var person1 = {
 _name: "Nicholas",
  get name() {
 console.log("Reading name");
 return this._name;
 },

  set name(value) {
 console.log("Setting name to %s", value);
 this._name = value;
 }
};
console.log(person1.name); // "Reading name" then "Nicholas"
person1.name = "Greg";
console.log(person1.name); // "Setting name to Greg" then "Greg"

This example defines an accessor property called name. There is a data
property called _name that contains the actual value for the property u.
(The leading underscore is a common convention to indicate that the
property is considered to be private, though in reality it is still public.)
The syntax used to define the getter v and setter w for name looks a lot
like a function but without the function keyword. The special keywords get
and set are used before the accessor property name, followed by parentheses and a function body. 
Getters are expected to return a value, while
setters receive the value being assigned to the property as an argument.
Even though this example uses _name to store the property data, you
could just as easily store the data in a variable or even in another object.
This example simply adds logging to the behavior of the property; there’s
usually no reason to use accessor properties if you are only storing the
data in another property—just use the property itself. Accessor properties
are most useful when you want the assignment of a value to trigger some
sort of behavior, or when reading a value requires the calculation of the
desired return value.