I am a beginner in javascript. Can someone explain the use of 'this' keyword in the following code and why the code doesn't work without the 'this' keyword?

function Count() {
  var count = 0;
  this.incrementCount = () => {
    count++;
    console.log(count);
  };

  this.decrementCount = () => {
    count--;
    console.log(count);
  };
}

var count1 = new Count();
count1.incrementCount();
count1.decrementCount();