ToDoItem.prototype.toString = function() {
  let mm = this.dueDate.getMonth() + 1;
  let dd = this.dueDate.getDate();

  if (this.finishedDate === undefined) {
    return '  ' + this.text + ' ' + mm + '/' + dd + '/' + this.dueDate.getFullYear();
  } if (this.finishedDate <= this.dueDate) {
    let mm1 = this.finishedDate.getMonth() + 1;
    let dd1 = this.finishedDate.getDate();
    return '  ' + this.text + ' ' + mm + '/' + dd + '/' + this.dueDate.getFullYear() + ' ' + mm1 + '/' + dd1 + '/' + this.finishedDate.getFullYear();
  }if (this.finishedDate > this.dueDate) {
    let mm2 = this.finishedDate.getMonth() + 1;
    let dd2 = this.finishedDate.getDate();
    return '* ' + this.text + ' ' + mm + '/' + dd + '/' + this.dueDate.getFullYear() + ' ' + mm2 + '/' + dd2 + '/' + this.finishedDate.getFullYear();
  }
};