# Getters and Setters

# get

Let's see how to create a get in JavaScript 😉

I am going to create a Car class with two properties:

• manufacturer
• productionYear

class Car {
  constructor(manufacturer, productionYear) {
    this.manufacturer = manufacturer;
    this.productionYear = productionYear;
  }
}

Now, I would like to know the age of this car (in years).

I can make a get for the age:

get age() {
  var currentDate = new Date();
  var currentYear = currentDate.getFullYear();
  return currentYear - this.productionYear;
}

Let's make a car 🚗 and get it's age:

var ferrari = new Car('Ferrari', 2015);
console.log(`${ferrari.age} years`);

And it makes sense to have age as a get property: we need to perform some computations (calculations) based on other properties (in our case productionYear).

So, it's not a static property, but a dynamic one.

# What about methods?

Now, this could have been a normal method:

getAge() {
  var currentDate = new Date();
  var currentYear = currentDate.getFullYear();
  return currentYear - this.productionYear;
}

And then we could call it:

var ferrari = new Car("Ferrari", 2015);
var ferrariAge = ferrari.getAge();
console.log(`${ferrariAge} years`);

But you can see that we need to use the () parantheses because it's a method call and to make it more descriptive, I chose to add an extra variable to hold the age.

With getters, the code looks better, it's more descriptive and we don't need the parantheses treating a computational property as a regular one.

# set

In contrast to get which returns a value, set assigns a value.

We are going to add a new requirement: the year must be after 1900.

Right now, we can change the year how we want:

var ferrari = new Car('Ferrari', 2015);
ferrari.productionYear = 12;
console.log(`${ferrari.age} years`);

And we get:

1518 years

A little bit too old, right? 😬

This is where we can restrict what value we get set / assign to the productionYear property by creating a *setter:

set productionYear(value) {
  if (value > 1900) {
    this._productionYear = value;
  }
}

Also, we need to add the getter for this property:

get productionYear() {
  return this._productionYear;
}

Now, whenever we try to assign a value to the productionYear property, this setter is called and we allow years that are after 1900.

var ferrari = new Car('Ferrari', 2015);
ferrari.productionYear = 12;
console.log(`${ferrari.age} years`); // 3 years

The productionYear remains unchanged. So, we have successfully managed to restrict what values we can assign to this property.

Also, we can throw an exception to tell the consumer of this class what happens:

set productionYear(value) {
  if (value < 1900) {
    throw 'Year must be after 1900';
  }
  this._productionYear = value;
}

Now, if we try to assign 12, it prints an error:

uncaught exception: Year must be after 1900

We can handle this, by using a try catch block:

try {
  var ferrari = new Car('Ferrari', 2015);
  ferrari.productionYear = 12;
} catch (error) {
  console.log(error);
}

console.log(`${ferrari.age} years`);

In this way, we are unable to change the value of the productionYear until the value is right.

Check the code in this CodePen.