https://code.google.com/archive/p/microajax/
So, in your HTML page simply include this script and do the calls with onClick of your button :
<html><head><script src='/microajax.js' type='text/javascript'></script></head><body>
<input type='button' style='width:100px;height:30px' value='LED_ON' onClick="microAjax('/TurnOnLED', function(res) { } );" /><br>
<input type='button' style='width:100px;height:30px' value='LED_OFF' onClick="microAjax('/TurnOffLED', function(res) { } );" /><br>
</body></html>