JavaScript Constructor functions Declaring a constructor function
Example
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; // Returns "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(); // Outputs "Meow" to the console
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 // 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 // Returns "true"
