Publish javascript variable to ROS

edit

Hi

I am having trouble publishing a variable to ROS from a javascript. I have made a button and a slider.

<input type="range" id="expoRange" value="127" min="0" max="255">
<button style="width:150px" onclick="expoFunction()">Set exposition</button><p id="showRange">N/A</p>

When the button is pressed it is suposed to publish the value of the slider to ROS. The value is put into the variable showRange and is displayed fine in the browser, but it is never published to ROS.

var exposition = new ROSLIB.Topic({
ros : ros,
name : '/fmInformation/stereo_camera/exposition',
messageType : 'std_msgs/UInt8' 
});

var expo_msg = new ROSLIB.Message({
  data : "showRange"
});

exposition.publish(expo_msg);

<script>
function expoFunction() {
    var expoVar = document.getElementById("expoRange").value;
    document.getElementById("showRange").innerHTML = expoVar;
}
</script>

I can also publsh a fixed number to ROS by assigning a number to the data field of expo_msg, but i dont know how to assign a variable to it. Here is my code in its entirety