Getters And Setters

Getters

Getters return the value of a property. They may also make a small modification of the returned result.

Let's look the following example:

class Square { get area() { console.log('calling getter'); return this.side * this.side; } } let square = new Square(); square.side = 3; console.log(square.area);

Output:

calling getter 9

Setters

Setters allow for a property to be modified. They are important since they can provide validation before a value is set.

Together getters and setters can control access and modification of a class member.

Let's look at the following example:

class Person { get name() { return this._name; } get age() { return this._age; } // basic setter function: set name(nameValue) { this._name = nameValue; } // setter function with validation: set age(ageValue) { if (ageValue < 0) { this._age = 0; return; } this._age = ageValue; } printData() { console.log("Name: " + this.name); console.log("Age: " + this.age); } } let person = new Person(); person.name = "Emily"; person.age = 20; // person.age = -1; person.printData();

Output:

Name: Emily Age: 20

Explanation:

• Value of the private member name is modified at line 21 without any validation.
• At lines 25 - 33 is defined a setter that has validation. If the validation fails a value of 0 is set at line 28. If validation passes (age >= 0) then the passed value is set (line 32).
• If we uncomment line 44 then the person object's age will have a value of zero. That's due to the validation at line 26.
• Notice that the additional members (_name and _age) are used inside the class body.
• Basically the getters and setters for name and age access / modify the _name and _age.
• if at line 5 _name is replaced with name, then a recursion will be formed. That's the reason why properties with _ prefix are used.
• Generally properties with _ prefix are meant to be accessed only inside the class body.

Why using getters and setters?

Because private members can have validation before modification (setter) and controlled access (getter).

It seems easier to have only public members. This way there is no need for getters and setters. It's a better practice to have private members that are accessed with getter and modified through setter. This way a validation can be provided in a setter and the public access can be done only to some members - those which have getters.