function Counter() {
  this.count = 0;
  this.increaseCount = function() {
    this.count++;
  }
  this.displayCount = function() {
    console.log(this.count);
  }
}
var counter1 = new Counter();
counter1.increaseCount = function() {
  this.count += 2;
}
counter1.increaseCount();
counter1.displayCount(); // 2