JavaScript constructor function is a special method to create and initialize an object instance. Use the new keyword to create an object from a constructor function.
constructor() { /* ... */ }
constructor(argument0) { /* ... */ }
constructor(argument0, argument1) { /* ... */ }
constructor(argument0, argument1, ... , argumentN) { /* ... */ }Recommended naming constructor functions with an upper-case first letter.
JavaScript constructor function
Simple example code of object constructor function.
<!DOCTYPE html>
<html>
<body>
<script>
// constructor function
function Person () {
this.name = 'John',
this.age = 23
}
// create an object
const p1 = new Person();
p1.name = "Mike"
p1.age = "100"
console.log(Person)
console.log(p1)
</script>
</body>
</html> Output:
Create Multiple Objects with Constructor Function
// create objects
const p1= new Person();
const p2= new Person();JavaScript this Keyword
The this keyword is used in a constructor function, where it refers to the object when the object is created.
// constructor function
function Person () {
this.name = 'John',
}
// create object
const person1 = new Person();
// access properties
console.log(person1.name); // JohnConstructor Function Parameters
You can also create a constructor function with parameters.
function Car(make, model, year) {
this.make = make;
this.model = model;
this.year = year;
}
// Creating instances of the Car object with different parameters
var car1 = new Car('Toyota', 'Camry', 2021);
var car2 = new Car('Honda', 'Civic', 2022);
console.log(car1.make); // Output: 'Toyota'
console.log(car2.year); // Output: 2022
In JavaScript, constructor functions can accept parameters just like regular functions. These parameters are used to initialize the properties of the objects created by the constructor. When you create an instance of a constructor function using the new keyword, you can pass arguments to the constructor, and those arguments will be used to set the initial state of the object.
Adding a Property to a Constructor
Person.nationality = “English”;
To add a new property to a constructor, you must add it to the constructor function:
function Person(first, age) {
this.firstName = "AAA";
this.age = 25;
this.nationality = "XYZ";
}Adding a Method to a Constructor
Constructor function can also define methods:
function Person(first, age) {
this.firstName = "AAA";
this.age = 25;
this.nationality = "XYZ";
this.name = function() {
return this.firstName;
};
}Built-in JavaScript Constructors
new String() // A new String object
new Number() // A new Number object
new Boolean() // A new Boolean object
new Object() // A new Object object
new Array() // A new Array object
new RegExp() // A new RegExp object
new Function() // A new Function object
new Date() // A new Date object Comment if you have any doubts or suggestions on this JS constructor topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version