This gist show an example of constructor function.

constructorFunction.js

let Person = function(first_name,last_name) {
      this.first_name = first_name;
      this.last_name = last_name;
  }
Person.prototype.getFullName = function() {
  return `Full Name is: ${this.first_name} ${this.last_name}`;
}

let personA = new Person('lorem','ipsum');
let personB = new Person('felis','ullamcorper');

personA.getFullName();
//Output: Full Name is: lorem ipsum
// In each instance personA,personB getFullName function is shared means when personA.getFullName() is called, the javascript engine 
// first will look in personA object if it is not found there then it will look in the personA parent that is Person.prototype from where it get 
// resolved