Default Constructor in JavaScript Last Updated : 23 Jan, 2024 Summarize Comments Improve Suggest changes Share Like Article Like Report In JavaScript, a default constructor is not explicitly defined like in some other programming languages such as Java or C++. In JavaScript, objects can be created without a formal constructor. When you create an object using the new keyword along with a constructor function, that function serves as the constructor for the object. If you don't provide a constructor function, JavaScript still creates an object for you, and it essentially has an "invisible" default constructor. Syntaxconstructor() {}Syntax(derived class) constructor(...args) { super(...args);}Example 1: Here, the constructor function of the Person class initializes the properties name and age with default values. When you create an instance of Person without passing any arguments, the default values are used. JavaScript class Person { constructor() { // Default values or optional initialization this.name = 'DefaultName'; this.age = 0; } sayHello() { console.log(`Hello, my name is ${this.name} and I am ${this.age} years old.`); } } // Creating an instance const person = new Person(); // Calling the method person.sayHello(); OutputHello, my name is DefaultName and I am 0 years old. Example 2: Here, the Dog class extends the Animal class. The Dog class's constructor uses the spread operator ...args to accept any number of arguments, and then it calls super(...args) to invoke the constructor of the superclass (Animal in this case). This allows the Dog class to initialize its own properties (breed) and inherit the properties from the Animal class (legs). The default values are used if no arguments are provided. JavaScript class Animal { constructor(legs) { this.legs = legs; } displayLegs() { console.log(`I have ${this.legs} legs.`); } } class Dog extends Animal { constructor(...args) { super(...args); this.breed = args[0] || 'Unknown Breed'; } bark() { console.log('Woof, woof!'); } displayInfo() { console.log(`I am a ${this.breed} with ${this.legs} legs.`); } } // Creating an instance const dog = new Dog(4, 'Golden Retriever'); // Calling methods dog.displayLegs(); dog.bark(); dog.displayInfo(); OutputI have 4 legs. Woof, woof! I am a 4 with 4 legs. Comment More infoAdvertise with us Next Article JavaScript Function() Constructor A amanv09 Follow Improve Article Tags : JavaScript Web Technologies Similar Reads JavaScript Function() Constructor The JavaScript Function() constructor is used to create new function objects dynamically. By using the Function() constructor with the new operator, developers can define functions on the fly, passing the function body as a string. This allows for greater flexibility in situations where functions ne 2 min read JavaScript Generator() Constructor In JavaScript, there is no particular Generator() constructor but instead, we can use generator function declaration to construct a Generator object which is iterable as the Generator object is a subclass of the Iterable class. Generators are usually used to create functions that can be exited and r 1 min read JavaScript Error() constructor Javascript Error() constructor is used to create a new error object. Error objects are arising at runtime errors. The error object also uses as the base object for the exceptions defined by the user. Syntax: new Error([message[, fileName[, lineNumber]]]) Parameters: message: It contains information 2 min read JavaScript Intl DisplayNames() Constructor JavaScript Intl.DisplayNames Constructor is used for creating Intl.DisplayNames object. This constructor is created using the new keyword. If we create the constructor without the new keyword it will give a TypeError Syntax: new Intl.DisplayNames(loc, opt) Parameters: It has two parameters both are 2 min read JavaScript Date constructor Property JavaScript Date constructor property returns the constructor function for an object. It is an ES1 feature and is supported by all browsers. The function which is returned by this property is just the reference to this function, not a date containing the functionâs name. The JavaScript date construct 2 min read What is a Constructor in JavaScript? A constructor in JavaScript is a special function that is used to create and initialize objects. When we want to create multiple objects with similar properties and methods, the constructor is used as a blueprint to create similar objects. This is useful when you want to create multiple objects with 8 min read Like