XMLHttpRequest passing a variable to php script

Question

I am trying to pass a variable to a php script using XMLHttpRequest and then have the php echo it back. I can't understand why it isn't working, could someone please help me. Here is the Javascript.

<script language="javascript" type="text/javascript">
    // Browser Support 
function Heatctrl(heatMode){
    var heatControlRequest;

    try{
        //Good Browsers
        heatControlRequest = new XMLHttpRequest();
    } catch (e) {
        //Internet Explorer
        try{
            heatControlRequest = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try{
                heatControlRequest = new ActiveXObject("Microsoft.XMLHTTP");
            }catch (e) {
                alert("Brower not supported");
                return false;
            }
        }
    }


    // Function to receive data from server and store in variable
    heatControlRequest.onreadystatechange = function(){
        if (heatControlRequest.readystate == 4){
            alert(heatControlRequest.responseText);
            //document.getElementById("controlMode").innerHTML=heatControlRequest.responseText;
            //var heatControlResponse = heatControlRequest.responseText;
        }
    }
    var url = "heatControl.php?heatmode="+heatMode;
    // Send the request
    heatControlRequest.open("GET", url, true);
    heatControlRequest.send();
}   
</script>

The HTML

    <div id="boilerButtons">
    <button type="button" onclick="Heatctrl('On')">Heating On</button>
    <button type="button" onclick="Heatctrl('Off')">Heating Off</button>
    <button type="button" onclick="Heatctrl('Boost')">Boost</button>
</div>

and the php

<?php
$controlMode = $_GET['heatmode'];
echo $controlMode; 
?>

Any help is much appreciated, I work in electronics not programming and I've been struggling with this now for two days.

What's "not working"? Is a request being made? Are there errors in your JavaScript console? Is your Heatctrl function being ran? — gen_Eric
– gen_Eric, Commented Nov 27, 2012 at 16:37
P.S. Don't use language="javascript" in your <script> tag. — gen_Eric
– gen_Eric, Commented Nov 27, 2012 at 16:39

ServerBloke · Accepted Answer · 2012-11-27 16:41:57Z

3

The problem is this line:

if (heatControlRequest.readystate == 4){
                            ^ this should be an uppercase S

It should be:

if (heatControlRequest.readyState == 4){

From the docs:

The XMLHttpRequest object can be in several states. The readyState attribute must return the current state.

answered Nov 27, 2012 at 16:41

ServerBloke

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2 Comments

ironcrow Over a year ago

Yay that worked, thank you so much. Just out of interest, is there any reason why this didn't show up as an error in Chrome's javascript console?

ServerBloke Over a year ago

You're welcome. Javascript allows you to check the value of undefined properties of an object like this without throwing an error.

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