Avinash.tech(…)

The constructor method is a special method for creating and initialising an object created within a class. When it comes to JS the syntax is slightly different as you can see in the example snippet below

class Task {
  constructor(name) {
    this.name = name;
    this.completed = false;
  }

  complete() {
    console.log("Completing task " + this.name);
  }

  save() {
    console.log("Saving task " + this.name);
  }
}

var task1 = new Task("task1");
task1.save(); //output: Saving task task1
task1.complete(); //output: Completing task task1

If one runs the above code through a transpiler like Babel for browser compatibility, the following code would be generated. Also notice that creating methods inside the Task function is a bad idea as it creates replication of method each time an instance is created.

var Task = function(name) {
  this.name = name;
  this.completed = false;
  this.save = function() {
    console.log(
      "Not a good idea as it replicates the method among all instances"
    );
  };
};

Task.prototype.save = function() {
  console.log("Saving task " + this.name);
};

Task.prototype.complete = function() {
  console.log("Completing task " + this.name);
};

var task1 = new Task("task1");
task1.save(); //output: Saving task task1
task1.complete(); //output: Completing task task1

Hope this clears some of the doubts on Constructor. p.s : Constructor has been added post EcmaScript 2015.