Constructor

Constructor is used for object creation and specifying some attributes. Look at this statement:


              1
            
student = new Student();

Student() is a constructor of class Student, so the student variable is now a Student object.

This simple constructor is using by default and creates an object only. But you can define a constructor that will initialize some object attributes.


              1
            
student = new Student('Robert', 22);

student object now has name Robert and age 22.

The syntax of the constructor inside the class is following:


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class Student{
  name;
  university;
  age;
  gpa;

  constructor(name, age){
    this.name = name;
    this.age = age;
  console.log('Student created');
  }

  sleep(){
    console.log('I am sleeping right now!');
  }
  happyBirthday(){
    this.age += 1;
    console.log('Today is my birthday');
  }
}

student = new Student('Robert', 22);

By object creating, you can pass some arguments and use them inside constructor. But note that skipped parameters will have undefined value. Look at the example and run it to see what happens.


              123456789101112131415
            
class Student{
  name;
  age;
  gpa;
  constructor(name, age, gpa){ // constructor with 3 parameters
    this.name = name;
    this.age = age;
    this.gpa = gpa;
    console.log('Student created');
  }
}

student = new Student('Robert', 22); // pass only 2 values
console.log(JSON.stringify(student));
// object has only 2 defined properties name and age

Only name and age properties are defined in student object because of 2 arguments while student initialization.

Pass the arguments in order they are defined in constructor.

Opgave

Swipe to start coding

Extend existing constructor with arguments for university and gpa attributes. After that, change the line of object initialization by adding 2 more arguements inside Student() statement.

Løsning

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Var alt klart?

Tak for dine kommentarer!

Sektion 1. Kapitel 6

Constructor

Constructor is used for object creation and specifying some attributes. Look at this statement:


              1
            
student = new Student();

Student() is a constructor of class Student, so the student variable is now a Student object.

This simple constructor is using by default and creates an object only. But you can define a constructor that will initialize some object attributes.


              1
            
student = new Student('Robert', 22);

student object now has name Robert and age 22.

The syntax of the constructor inside the class is following:


              12345678910111213141516171819202122
            
class Student{
  name;
  university;
  age;
  gpa;

  constructor(name, age){
    this.name = name;
    this.age = age;
  console.log('Student created');
  }

  sleep(){
    console.log('I am sleeping right now!');
  }
  happyBirthday(){
    this.age += 1;
    console.log('Today is my birthday');
  }
}

student = new Student('Robert', 22);

By object creating, you can pass some arguments and use them inside constructor. But note that skipped parameters will have undefined value. Look at the example and run it to see what happens.


              123456789101112131415
            
class Student{
  name;
  age;
  gpa;
  constructor(name, age, gpa){ // constructor with 3 parameters
    this.name = name;
    this.age = age;
    this.gpa = gpa;
    console.log('Student created');
  }
}

student = new Student('Robert', 22); // pass only 2 values
console.log(JSON.stringify(student));
// object has only 2 defined properties name and age

Only name and age properties are defined in student object because of 2 arguments while student initialization.

Pass the arguments in order they are defined in constructor.

Opgave

Swipe to start coding

Extend existing constructor with arguments for university and gpa attributes. After that, change the line of object initialization by adding 2 more arguements inside Student() statement.

Løsning

Skift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder

Var alt klart?

Tak for dine kommentarer!

Sektion 1. Kapitel 6

Skift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder