what is the purpose of a constructor in javascript code example

Example 1: constructor in js

A constructor is a function that creates an instance of a class
  which is typically called an “object”. In JavaScript, a constructor gets 
  called when you declare an object using the new keyword.
  The purpose of a constructor is to create an object and set values if 
  there are any object properties present.

Example 2: function constructor in js

// The Function constructor creates a new Function object. 
// Calling the constructor directly can create functions dynamically
// It creates global functions unlike eval.

new Function(arg1, functionBody)
new Function(arg1, arg2, functionBody)
new Function(arg1, ... , argN, functionBody)

Example 3: how to create a constructor in javascript

function Bird() {
  this.name = "Albert";
  this.color  = "blue";
  this.numLegs = 2;
}

let blueBird = new Bird();