如何在页面刷新时递增一个值？

<span id="counter">0</span>

window.onload = function() {
  var counterElement = document.getElementById('counter');
  var counterValue = parseInt(counterElement.innerHTML);
  counterValue++;
  counterElement.innerHTML = counterValue;
}

var counter = 0;

app.get('/counter', function(req, res) {
  counter++;
  res.send(counter.toString());
});

window.onload = function() {
  fetch('/counter')
    .then(response => response.text())
    .then(counterValue => {
      var counterElement = document.getElementById('counter');
      counterElement.innerHTML = counterValue;
    });
}