What is a constructor in js code example

Example 1: javascript constructor function

function ClassMates(name,age){
  this.name=name;
  this.age=age;
  this.displayInfo=function(){
    return this.name + "is " + this.age + "year's old!";
  }
}

let classmate1 = new ClassMates("Mike Will", 15);
classmate.displayInfo(); // "Mike Will is 15 year's old!"

Example 2: 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 3: how to create a constructor in javascript

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

let blueBird = new Bird();

Example 4: why do we use Object Constructors

function Tree(name) {
  this.name = name
}

let theTree = new Tree('Redwood')
console.log('theTree.constructor is ' + theTree.constructor)