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Javascript Constructor functions

Constructor functions are functions designed to construct a new object. Within a constructor function, the keyword this refers to a newly created object which values can be assigned to. Constructor functions "return" this new object automatically.


function Cat(name) {
 this.name = name;
 this.sound = "Meow";
}

Constructor functions are invoked using the new keyword:


let cat = new Cat("Tom");
cat.sound; 

Output

"Meow"

Constructor functions also have a prototype property which points to an object whose properties are automatically inherited by all objects created with that constructor:


Cat.prototype.speak = function() {
 console.log(this.sound);
}
cat.speak();

Output

"Meow"

Objects created by constructor functions also have a special property on their prototype called constructor, which
points to the function used to create them:


cat.constructor

Output

Returns the `Cat` function

Objects created by constructor functions are also considered to be "instances" of the constructor function by the
instanceof operator:


cat instanceof Cat

Output

"true"


Conclusion

In this page (written and validated by ) you learned about Javascript Constructor functions . What's Next? If you are interested in completing Javascript tutorial, your next topic will be learning about: Javascript Loops.



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