Classes
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Expert Answer & Key Takeaways
Mastering Classes is essential for high-fidelity technical architecture and senior engineering roles in 2026.
JavaScript Classes
ECMAScript 2015, also known as ES6, introduced JavaScript Classes. JavaScript Classes are templates for JavaScript Objects.
1. JavaScript Class Syntax
Use the keyword
class to create a class. Always add a method named constructor():class Car {
constructor(name, year) {
this.name = name;
this.year = year;
}
}2. The Constructor Method
The constructor method is a special method:
- It has to has the exact name "constructor".
- It is executed automatically when a new object is created.
- It is used to initialize object properties.
const myCar1 = new Car("Ford", 2014);
const myCar2 = new Car("Audi", 2019);3. Class Inheritance
To create a class inheritance, use the
extends keyword. A class created with a class inheritance inherits all the methods from another class.class Model extends Car {
constructor(brand, mod) {
super(brand);
this.model = mod;
}
show() {
return this.present() + ', it is a ' + this.model;
}
}[!IMPORTANT] Thesuper()method refers to the parent class. By calling thesuper()method in the constructor method, we call the parent's constructor method and gets access to the parent's properties and methods.
4. Class Methods
Class methods are created with the same syntax as object methods:
class Car {
constructor(name, year) {
this.name = name;
this.year = year;
}
age() {
const date = new Date();
return date.getFullYear() - this.year;
}
}Top Interview Questions
?Interview Question
Q:Are JavaScript classes hoisted?
A:
No. Unlike functions, class declarations are NOT hoisted. You must define a class before you can instantiate it using the 'new' keyword.
?Interview Question
Q:What is the purpose of the constructor() method?
A:
The constructor is a special method used to initialize an object's state when it is created. It is automatically called when you use the 'new' operator.
?Interview Question
Q:What does the 'super' keyword do?
A:
In a derived class (using extends), super refers to the parent class. It is used to call the parent's constructor and to access methods on the parent object.
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