Introduction
So we learned earlier what is a class and what is an object, now we'll learn about the structure of a class.
Structure of a class
A class is a blueprint for creating objects, it defines a set of attributes that will characterize any object of the class. The attributes are called fields
or properties
or attributes
, and list of actions are called methods
.
So a class is a definition of a type, it defines the characteristics and the actions of the type.
Class Attributes
As we said it is also called properties
or fields
but in JS/TS we call it attributes
or properties
, so what are attributes?
Attributes are the characteristics of a class, for example the Human
class has the attributes name
, age
, gender
, height
, weight
, etc.
Class Methods
Methods are the actions of a class, for example the Human
class has the methods walk
, talk
, eat
, sleep
, etc.
They represent the behaviors of a class.
Our First Class
Let's create our first class, we'll create a class called Human
, and we'll add the attributes name
, age
, gender
, height
, weight
, etc.
class Human {
name;
age;
gender;
height;
weight;
}
So the class is defined using class
keyword, then the name of the class, then the attributes are defined using the ;
semicolon.
Creating an object
Now we'll create an object of the Human
class, we'll create an object called me
.
class Human {
name;
age;
gender;
height;
weight;
}
const me = new Human();
To create a new object from a class, we must use the new
keyword, then the name of the class.
The class can be called with or without parenthesis ()
, but it is recommended to use parenthesis
.
So we created an object of the Human
class, and we assigned it to the variable me
.
Assigning values to attributes
Now we'll assign values to the attributes of the Human
class.
class Human {
name;
age;
gender;
height;
weight;
}
const me = new Human();
me.name = "Hasan";
me.age = 25;
me.weight = 70;
me.height = 180;
me.gender = 'male';
If you notice that syntax, it is the same syntax as we write with normal object
, why? because it is literally an object, it is just a class that defines the type of the object.
Class Constructor
The constructor is a special method that is called when an object is created from a class, it is used to initialize the object.
class Human {
name;
age;
gender;
height;
weight;
constructor(name) {
this.name = name;
}
}
So we created a constructor, and we passed the name
parameter to it, and we assigned the name
parameter to the name
attribute.
Now let's see how to use it.
class Human {
name;
age;
gender;
height;
weight;
constructor(name) {
this.name = name;
}
}
const me = new Human("Hasan");
Here we passed the Hasan
string to the constructor, and it assigned it to the name
attribute.
In that sense, we can say that we created a new Human (Class)
which is me (Object)
and we passed the Hasan
string to the constructor, and it assigned it to the name
attribute.
Using Class Methods
Now we'll create a method called walk
in the Human
class.
class Human {
name;
age;
gender;
height;
weight;
constructor(name) {
this.name = name;
}
walk() {
console.log(`${this.name} is walking`);
}
}
const me = new Human("Hasan");
me.walk(); // Hasan is walking
So we created a method called walk
, and we called it using the me
object.
It will output in the console Hasan is walking
.
Assigning values to attributes using methods
Actually, we can assign a value to any property (attribute/field)
we want, but it is not recommended to do that, because it will make the code messy.
So we'll create a method called setAge
in the Human
class to define the age of the me
object.
class Human {
name;
age;
gender;
height;
weight;
constructor(name) {
this.name = name;
}
walk() {
console.log(`${this.name} is walking`);
}
setAge(age) {
this.age = age;
}
}
const me = new Human("Hasan");
me.setAge(25);
In the above sample of code, we created a method called setAge
, and we passed the 25
number to it, and it assigned it to the age
attribute.
Getting values from attributes using methods
We can also create a method to get the value of an attribute, for example we'll create a method called getAge
in the Human
class to get the age of the me
object.
class Human {
name;
age;
gender;
height;
weight;
constructor(name) {
this.name = name;
}
walk() {
console.log(`${this.name} is walking`);
}
setAge(age) {
this.age = age;
}
getAge() {
return this.age;
}
}
const me = new Human("Hasan");
me.setAge(25);
console.log(me.getAge()); // 25
Here we created a method called getAge
, and it returned the value of the age
attribute.
π¨ Conclusion
In this lesson, we learned about the structure of a class, and we learned how to create a class, and how to create an object from a class, and how to assign values to attributes, and how to create methods, and how to use them.
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