JavaScript and AJAX are showing an error message that says: "ReferenceError: x is not

I am currently working on a jQuery function that retrieves the value from a PHP-generated checkbox and sends it through AJAX. The value being sent is always a single word consisting only of letters. Here is the script I have written:

<script type="text/javascript">
    $(document).ready(function() {
        $("input:checkbox").on("click", function () {
            step = this.value;
            //document.getElementById("test").innerHTML = step;
            responseArray = [];

            xmlhttp=new XMLHttpRequest();
            xmlhttp.onreadystatechange=function() {
                if (xmlhttp.readyState==4 && xmlhttp.status==200) {
                    responseArray = eval("(" + xmlhttp.responseText + ")");
                    document.getElementById("test").innerHTML = responseArray;
                }
            }

            xmlhttp.open("GET", "checkbox.php?step="+step, true);
            xmlhttp.send();
        });
    });
</script>

However, when executing the above code, I encounter the error "ReferenceError: [this.value] is not defined." It's worth mentioning that [this.value] represents the actual dynamic value based on the selected checkbox. Interestingly, in line 5 of the code snippet, the correct value is displayed in the "test" element when uncommented. This leads me to believe that the issue arises after this point. Even simplifying the checkbox.php file down to its basic form results in the same error.

<?php       
    $step = $_GET["step"];
    echo "[" . $step . "]";
?>

Answer №1

It appears that you are utilizing Jquery, so using JQuery's AJAX object would be more efficient for the request:

$.ajax({
  url: 'checkbox.php?step=',
  success: function(data) {
    alert(data);
  }
});

http://api.jquery.com/jQuery.ajax/

The issue seems to lie in not correctly obtaining the value of the checkbox. Checkboxes are binary, either checked or unchecked. Here's how you can retrieve different parameters:

$(document).ready(function () {
    $("input:checkbox").on("click", function () {
        var checkboxID = $(this).attr("ID");        // Retrieves the ID of the checkbox
        var isChecked = $(this).is(':checked');     // Returns true or false

        alert($(this).attr("ID") + " is " + isChecked);
    });
});

Therefore, your final code may resemble:

$(document).ready(function () {
    $("input:checkbox").on("click", function () {
        var checkboxID = $(this).attr("ID");        // Retrieves the ID of the checkbox
        var isChecked = $(this).is(':checked');     // Returns true or false

        $.ajax({
           url: 'checkbox.php?step=' + isChecked ,
           success: function(data) {
             alert(data);
           }
         });
    });
});

(untested code) which would send a request to the url checkbox.php?step=true

Greetings from another coding enthusiast! :D

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