Constructors

Constructor is used to create objects. It is a function that executes when object is created.

There are different types of constructors.

Syntax

Defining constructor:

constructor(args) { // code }

Default Constructor

Default constructor does not accept any arguments. It can be used without defining it.

If defined it sets default values to class members.

Example of default constructor usage without defining it:

class Person { } let person = new Person(); person.name = "Smith"; person.age = 23; console.log("Name: " + person.name); console.log("Age: " + person.age);

Output:

Name: Smith Age: 23

An object is created via default constructor at line 5.

Example of defining and using default constructor:

class Person { constructor() { console.log('Object Creation'); this.name = "Unknown"; this.age = 0; } printData() { console.log('Name: ' + this.name); console.log('Age: ' + this.age); } } let person1 = new Person(); person1.printData(); let person2 = new Person(); person2.name = "Smith"; person2.age = 23; person2.printData();

Output:

Object Creation Name: Unknown Age: 0 Object Creation Name: Smith Age: 23

Explanation:

• The default constructor is defined at 2 - 7 lines .
• At line 15 and 18 an object is created via the default constructor. The code of the default constructor executes and "Object creation." is printed.
• person1 object does not overwrite name and age. It's properties have the same values as those set in the default constructor.

Parameterized Constructor

The parameterized constructor accepts parameters which usually are used to set value for the object's members.

Example of class using parameterized constructor:

class Person { constructor(name, age) { console.log('Object Creation'); this.name = name; this.age = age; } printData() { console.log('Name: ' + this.name); console.log('Age: ' + this.age); } } let personObj = new Person("John", 22); personObj.printData();

Output:

Object Creation Name: John Age: 22

Explanation:

• At lines 2 - 7 a parametrized constructor is defined.
• At line 15 an object is created via the parametrized constructor.