AJAX返回变量

Question

I'm trying to POST a variable through a select box, which will submit the data through AJAX and then I need to be able to use that vairable on the original page, which updates the sql queries.

Here is the code I have got so far:

<script type="text/javascript">
function selectCategory() {

    document.getElementById('categoryText').addEventListener("change", function() {
        var xmlhttp=new XMLHttpRequest();
        xmlhttp.open("GET","/category.php?category3="
            +document.getElementById("categoryText").value, false);
        xmlhttp.send(null);
    });

}
</script>

and the AJAX (which im struggling with)

<?php 

    /*Retreving the Value from the select box */
    $categoryFilter = $_GET['category3']; 

?>

Answer 1

When you say "select box" do you mean a select menu - ie: dropdown? If that is the case then generally you access the value of the selected element like this:-

var oSel=document.getElementById("categoryText");
var value=oSel.options[ oSel.options.selectedIndex ].value

    <script type="text/javascript">
        function selectCategory() {
            var oSel=document.getElementById('categoryText')
            oSel.addEventListener("change", function() {
                var xmlhttp=new XMLHttpRequest();
                xmlhttp.open( "GET", "/category.php?category3="+this.options[ this.options.selectedIndex ].value, false );
                xmlhttp.send(null);
            }.bind( oSel ) );
        }
        selectCategory.call( this );
    </script>