Overriding valueOf in custom objects

overriding_valueOf.js

function Counter(){
  this.count = 0;
}
 
Counter.prototype.incr = function() {
  this.count++;
}
 
Counter.prototype.valueOf = function() {
  return this.count;
}
 
c = new Counter();
 
c.incr(); // this.count now === 1;
 
console.log(c.count); // will return 1;
 
console.log(c + 2); // will return 3