text: function func_num(value) {
      let exponent = document.getElementById('exponent_td');
      if (Number.parseInt(exponent.innerText) === 0) {
          exponent.innerText = value;
      } else {
          exponent.innerText = exponent.innerText + value;
      }
  }
  
  function clean() {
      let exponent = document.getElementById('exponent_td');
      let result = document.getElementById('result');
      exponent.innerText = 0;
      result.innerText = 0;
  }
  
  function equals() {
      let exponent = document.getElementById('exponent_td');
      let result = document.getElementById('result');
      try {
          result.innerText = eval(exponent.innerText);
      } catch (e) {
          result.innerText = NaN;
      }
  }
  
  function func_oper(value) {
      let exponent = document.getElementById('exponent_td');
      exponent.innerText = exponent.innerText + value;
  }