[php] Pass Javascript Variable to PHP POST

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JavaScript post request like a form submit

I have a value calculated in JS that I'd like to pass as part of an input form to a PHP script. How can I get a value the JS value to the PHP as a POST parameter?

Basically, on submit, I need the total var to be passed via post to the next script.

The first idea that comes to mind is create an invisible input form that has the value in it and is inputted with the form, is that possible?

You can do this using Ajax. I have a function that I use for something like this:

function ajax(elementID,filename,str,post)
{
    var ajax;
    if (window.XMLHttpRequest)
    {
        ajax=new XMLHttpRequest();//IE7+, Firefox, Chrome, Opera, Safari
    }
    else if (ActiveXObject("Microsoft.XMLHTTP"))
    {
        ajax=new ActiveXObject("Microsoft.XMLHTTP");//IE6/5
    }
    else if (ActiveXObject("Msxml2.XMLHTTP"))
    {
        ajax=new ActiveXObject("Msxml2.XMLHTTP");//other
    }
    else
    {
        alert("Error: Your browser does not support AJAX.");
        return false;
    }
    ajax.onreadystatechange=function()
    {
        if (ajax.readyState==4&&ajax.status==200)
        {
            document.getElementById(elementID).innerHTML=ajax.responseText;
        }
    }
    if (post==false)
    {
        ajax.open("GET",filename+str,true);
        ajax.send(null);
    }
    else
    {
        ajax.open("POST",filename,true);
        ajax.setRequestHeader("Content-type","application/x-www-form-urlencoded");
        ajax.send(str);
    }
    return ajax;
}

The first parameter is the element you want to change. The second parameter is the name of the filename you're loading into the element you're changing. The third parameter is the GET or POST data you're using, so for example "total=10000&othernumber=999". The last parameter is true if you want use POST or false if you want to GET.

Your idea of an hidden form element is solid. Something like this

<form action="script.php" method="post">
<input type="hidden" name="total" id="total">
</form>

<script type="text/javascript">
var element = document.getElementById("total");
element.value = getTotalFromSomewhere;
element.form.submit();
</script>

Of course, this will change the location to script.php. If you want to do this invisibly to the user, you'll want to use AJAX. Here's a jQuery example (for brevity). No form or hidden inputs required

$.post("script.php", { total: getTotalFromSomewhere });

There is a lot of ways to achieve this. In regards to the way you are asking, with a hidden form element.

create this form element inside your form:

<input type="hidden" name="total" value="">

So your form like this:

<form id="sampleForm" name="sampleForm" method="post" action="phpscript.php">
<input type="hidden" name="total" id="total" value="">
<a href="#" onclick="setValue();">Click to submit</a>
</form>

Then your javascript something like this:

<script>
function setValue(){
    document.sampleForm.total.value = 100;
    document.forms["sampleForm"].submit();
}
</script>