Question

I have some checkbox values that I generate as

$sql = "sql statement";
$courseResult = mysqli_query($connection, $sql);
$courses = mysqli_fetch_row($
// Display the courses the user has taken 
while ($courses) {
    echo "<td><input type='checkbox' name='coursesToAdd[]' id='coursesToAdd[]' value='$courses[0]'>$courses[0]</td></tr>";            
    $courses = mysqli_fetch_row($courseResult);
}

<input type='button' onclick='EditStudentCertificates()' value='Submit'/>

what i want to do is get the values that the user checks into an array, and than access this array from javascript which i was trying to do as such, but it does not seem to work:

        function EditStudentCertificates(){                
            if (window.XMLHttpRequest){
                // code for IE7+, Firefox, Chrome, Opera, Safari                
                xmlhttp=new XMLHttpRequest();
            }
            else{
                // code for IE6, IE5
                xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
            }      

            var coursesToAddField = document.getElementById("coursesToAdd[]");
            var coursesToAdd = coursesToAddField ? coursesToAddField.value : '';

            xmlhttp.open("POST","updateStudentCInfo.php",true);
            xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
            xmlhttp.send("certValue="+certValue+"&coursesToAdd="+coursesToAdd);
            window.alert("Your certificate information has been updated");
            window.location.reload();                
        }

What i think the problem is is something with the way i trying to get the values from the checkboxs in the javascript, possibly something with:

            var coursesToAddField = document.getElementById("coursesToAdd[]");
            var coursesToAdd = coursesToAddField ? coursesToAddField.value : '';

Because the variable coursesToAdd doesnt seem to hold anything but the value of the first checkbox on the page no matter how many checkboxes i check on the page before hitting submit.

Answer 1

As I mentioned in my comment above:

Without even looking at the AJAX code you posted, you are having a problem with the way you get the values from the checkboxes. You are using the same id coursesToAdd[] to all checkboxes. That is invalid, as all ids need to be unique on the page. You need to use a classname instead.

In your HTML/PHP:

while ($courses) {
    echo "<td><input type='checkbox' name='coursesToAdd[]' class='coursesToAdd' value='$courses[0]'>$courses[0]</td></tr>";            
}

And in your JS you can get to the checkboxes like this:

var courseCheckboxes = document.getElementsByClassName("coursesToAdd");
for (var i=0; i < courseCheckboxes.length; i++) {
    if (courseCheckboxes[i].checked) {
       // do something with the checkbox
    }
}