JavaScript class constructor Method is a special method used in classes to create and initialize an object instance of that class. This method is called automatically when a class is initiated.
constructor()
constructor(argument0, argument1, ... , argumentN)JavaScript will add an invisible and empty constructor method if you don’t add a constructor method in the class.
Note: You can’t use more than one constructor() method.
JavaScript class constructor
A simple example code constructor method must define before any other methods can be called on an instantiated object.
<!DOCTYPE html>
<html>
<body>
<script>
class Polygon {
constructor() {
console.log("Constructor Method")
this.name = 'Polygon';
}
}
const poly1 = new Polygon();
console.log(poly1.name);
</script>
</body>
</html> Output:
More Example
class Person {
constructor(name) {
this.name = name;
}
introduce() {
console.log(`Hello, my name is ${this.name}`);
}
}
const otto = new Person('Otto');
otto.introduce();Output: Hello, my name is Otto
A constructor can use the super keyword to call the constructor of the superclass.
function Animal(legs) {
this.legs = legs;
}
Animal.prototype.walk = function() {
console.log('walking on ' + this.legs + ' legs');
}
function Bird(legs) {
Animal.call(this, legs);
}
Bird.prototype = Object.create(Animal.prototype);
Bird.prototype.constructor = Animal;
Bird.prototype.fly = function() {
console.log('flying');
}
var pigeon = new Bird(2);
pigeon.walk();
pigeon.fly(); Do comment if you have any doubts or suggestions on this JS class topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version
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