text: 
  // "In range" with "has" trap 
  
  let range = {
    start : 1,
    end :10
  };
  range = new Proxy(range, {
    has(target, prop){
      return prop >= target.start && prop <= target.end;
    }
  });
  
  console.log(5 in range);   // true
  console.log(50 in range);   // false
  
  