text: function calculate(command, previousNumber, nextNumber) {
      var result;
      switch (command) {
          case 'add':
              return previousNumber + nextNumber;
          case 'substract':
              return previousNumber - nextNumber;
          case 'multiply':
              return previousNumber * nextNumber;
          case 'divide':
              return previousNumber / nextNumber;
          case 'remainder':
              return previousNumber % nextNumber;
      }
  }
  /*function calculate(action: string, previousNumber: number, nextNumber: number): number {
      let result: number;
      switch (action) {
          case 'add':
              result = previousNumber + nextNumber;
              break;
          case 'substract':
              result = previousNumber - nextNumber;
              break;
          case 'multiply':
              result = previousNumber * nextNumber;
              break;
          case 'divide':
              result = previousNumber / nextNumber;
              break;
          case 'remainder':
              result = previousNumber % nextNumber;
              break;
  
              return result;
      }
  }*/
  console.log(calculate('add', 1, 3)); // 4
  console.log(calculate('substract', 3, 1)); // 2
  console.log(calculate('multiply', 4, 2)); // 8
  console.log(calculate('divide', 4, 2)); // 2
  console.log(calculate('remainder', 5, 2)); // 1
  