Uncaught TypeError: setInterval(...) is not a function?

Uncaught TypeError: setInterval(...) is not a function
    at showCurrentValue (realtime_vis.js:88)
    at HTMLDocument.<anonymous> (realtime_vis.js:5)

function showCurrentValue(timeout) {
  (setInterval(fetch_request_realtime_data, timeout))();
}

function fetch_request_realtime_data() {
  fetch('./getRealTimeData').then((response) => response.json()
    .then((data) => {
      let text = JSON.stringify(data);
      updateCurrentData(text);
      return data;
    }));
}