Calling the actuator API is done slightly differently, since we use the POST method instead of the GET method. We need to send some content with the request. Sending text-based content is easy. We only need to send a string in the send() method. But we still need to set the Content-Type header to describe what type of text-based content we want to send. In our example, we use plain text:

var Span = document.getElementById("OutputState"); 
var CurrentState = Span.innerHTML; 
var xhttp = new XMLHttpRequest(); 
xhttp.onreadystatechange = function () 
{ 
   if (xhttp.readyState == 4) 
   { 
          if (xhttp.status == 200) 
          { 
                 var Data = JSON.parse(xhttp.responseText); 
                 Span.innerHTML = Data.output ? "ON" : "OFF"; 
          } 
 
          delete xhttp; 
   } 
}; 
 
xhttp.open("POST", "/Set", true); 
xhttp.setRequestHeader("Accept", "application/json"); 
xhttp.setRequestHeader("Content-Type", "text/plain"); 
if (CurrentState == "ON") 
   xhttp.send("OFF"); 
else 
   xhttp.send("ON"); 

The following image shows what our very simple user interface might look like in a browser: