<select id="myselect" onchange="change_myselect(this.value)">
  <option value="">Choose an option:</option>
  <option value="customers">Customers</option>
  <option value="products">Products</option>
  <option value="suppliers">Suppliers</option>
</select>

<script>
function change_myselect(sel) {
  const dbParam = JSON.stringify({table:sel,limit:20});
  const xmlhttp = new XMLHttpRequest();
  xmlhttp.onload = function() {
    const myObj = JSON.parse(this.responseText);
    let text = "<table border='1'>"
    for (let x in myObj) {
      text += "<tr><td>" + myObj[x].name + "</td></tr>";
    }
    text += "</table>"
    document.getElementById("demo").innerHTML = text;
  }
  xmlhttp.open("POST", "http://10.48.130.158:8080/zabbix.php?action=dashboard.view&dashboardid=1&from=now-1h&to=now");
  xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xmlhttp.send("x=" + dbParam);
}
</script>