The Ultimate Battle: JavaScript Class vs Function vs Constructor!

As a JavaScript developer, understanding the differences between classes, functions, and constructors is very important. Each has its very own use case and advantages. In our article, we are going to analyze JavaScript class vs function vs constructor, compare their features, and provide running examples that will help you choose the right alternative based to your needs.

What is a JavaScript Class?

JavaScript classes are a blueprint for creating objects. Help us to create multiple objects with similar properties and methods.

Key Features of JavaScript Classes

• Syntactic sugar: Classes provide a clearer and more concise syntax to create objects and deal with inheritance.
• Methods: Functions defined within classes.
• Inheritance: Easily create subclasses that inherit properties and methods from parent classes.

JavaScript Class: Feature List

Feature	Description
Class Syntax	Uses class keyword for definition
Constructor	Initializes new objects with constructor()
Inheritance	Extends classes using extends
Super Keyword	Calls methods from parent class
Static Methods	Functions called on the class itself
Instance Methods	Regular methods for instances
Getters/Setters	Control access to properties
Private Fields	Encapsulated data using # syntax
Method Overriding	Customizes inherited methods
Class Expressions	Dynamic class definitions
Prototype Inheritance	Uses prototypes for inheritance
Mixins	Combines functionality from multiple classes

Code Example

<script>
    class Person {
      constructor(name, age) {
        this.name = name;
        this.age = age;
      }

      greet() {
        console.log(`Hello, my name is ${this.name} and I am ${this.age} years old.`);
      }
    }

    const person1 = new Person('Shawpnendu Bikash', 45);
    person1.greet(); // Output: Hello, my name is Shawpnendu Bikash and I am 45 years old.
</script>

Output

Parts of a JS Class

So, now we have enough knowledge on JavaScrupt classes – right? Let us move on to our next section, named Javascript Functions.

What is a JavaScript Function?

Functions are one of the fundamental code blocks in JavaScript. They are reusable pieces of code, and we can call or execute this block of code whenever needed.

Key Features of JavaScript Functions

• Reusability: We can use this code block as many times as we need.
• Parameters: Accept inputs to work with.
• Return values: Output results.

JavaScript Functions: Feature List

Feature	Description
Function Declaration	Defines a named function with the function keyword.
Function Expression	Defines a function as part of a larger expression, can be anonymous or named.
Arrow Functions	Concise syntax with =>, does not have its own this context.
Parameters	Accepts inputs for the function, specified within parentheses.
Default Parameters	Allows setting default values for function parameters.
Rest Parameters	Gathers multiple arguments into a single array using … syntax.
Return Statement	Specifies the value that a function returns.
First-Class Functions	Functions can be treated as variables, passed as arguments, or returned.
Higher-Order Functions	Functions that take other functions as arguments or return them.
IIFE (Immediately Invoked Function Expression)	Functions that run as soon as they are defined.
Closures	Functions that remember the scope in which they were created.
Callback Functions	Functions passed into other functions to be called at a later time.
Async Functions	Declared with async, allows use of await for asynchronous operations.
Generator Functions	Declared with function, can pause execution and yield multiple values.
Function Scope	Variables declared within a function are local to that function.

Code Example

<script>
    function add(a, b) {
      // line of codes
      return a + b;
    }

    console.log(add(2, 3)); // Output: 5
</script>

Parts of a JS Function

What is a JavaScript Constructor?

A constructor is a special function. It is used to create and initialize an object in JavaScript. Basically, a constructor is defined within a class, but you can also define it as a standalone function.

Actually, constructors came first in JS and some years later classes were introduced. That’s why you found these two types of declarative variations. Don’t be confused.

Key Features of JavaScript Constructors

• Initialization: Set initial values for object properties.
• new keyword: Used to create instances of objects.
• Prototypes: Allow sharing methods among all instances.

JavaScript Constructors: Feature List

Feature	Description
Constructor Function	Special function used to create and initialize objects.
Class Constructor	Defined within a class using the constructor keyword.
Prototype Assignment	Methods and properties can be added to the constructor’s prototype.
this Keyword	Refers to the newly created object within the constructor.
Instance Creation	Instances are created using the new keyword.
Default Constructor	Automatically created if no constructor is defined in a class.
Constructor Overloading	Multiple constructors with different parameters are not supported natively.
Private Properties	Created using closures or symbols within constructor functions.
Inheritance	Achieved by calling a parent constructor within a child constructor using super().
Static Methods	Defined on the constructor function or class itself, not on instances.
Factory Functions	Alternative to constructors, returning objects without using new.
Constructors in Prototypes	Custom constructors can be linked to object prototypes.
ES6 Class Syntax	Provides a more straightforward way to create constructors compared to function syntax.
Instance Properties	Properties can be directly assigned within the constructor.
Error Handling	Constructors can include try-catch blocks for handling initialization errors.

Code Example

<script>
    function Car(brand, model) {
      this.brand = brand;
      this.model = model;
    }

    const myCar = new Car('Toyota', 'Corolla');
    console.log(myCar.brand); // Output: Toyota
</script>

Parts of JS Constructor

So far, I have tried my best to give you a basic understanding of JS classes, functions, and constructors. I hope you read carefully. To realize the differences among them, basic knowledge of each concept is necessary.

Here is a comparison table summarizing the differences and similarities between classes, functions, and constructors:

Comparing JavaScript Class vs Function vs Constructor

Feature	Class	Function	Constructor
Purpose	Blueprint for objects	Reusable piece of code	Initialize object properties
Syntax	class keyword	function keyword	function keyword
Instantiation	new keyword	Called directly	new keyword
Inheritance	Yes	No	Possible through prototypes
Reusability	Yes	Yes	Yes

When to Use Each One?

Use Classes When:

• You need to create multiple objects using the same set of properties and methods.
• Your solution needs inheritance and polymorphism support.
• You prefer a more structured and readable syntax.

Use Functions When:

• You just want to implement a reusable piece of code.
• Your solution does not require any object-oriented features.
• You want to keep your code modular and maintainable.

Use Constructors When:

• You need to initialize the object properties directly.
• You want to create instances of an object with the new keyword.
• You prefer the earlier way of object creation in JavaScript.

Conclusion

In summary, understanding the differences between JavaScript class vs function vs constructor is not so easy. Classes offer a more structured way of creating objects in JavaScript and support OOP as well. Functions provide reusable code blocks and constructors are useful for directly initializing object properties and are a traditional method for creating objects.

So choose the right one based on your customer business needs. Whether you are developing a complex application or a single page script, knowing when to use classes, functions, or constructors will help you achieve your goals correctly. Practice regularly and comply with all of code syntaxes rightly.