how can i retrieve a current value of textarea?

Problem : So I have alerted the value of textarea by:

var source = document.getElementById('source').value;
            alert(source);

But the value of textarea is alerted as it was at the time of page load. And I want to alert current value of the textarea. I have also tried

$("form").submit(function(){

But that also haven't helped me. So how can I do this?

This is my code.

<html>
    <head>
    <title>Perl WEB</title>
    <script type="text/javascript" src="http://code.guru99.com/Perl1/codemirror.js"></script>
    <link rel="stylesheet" href="http://code.guru99.com/Perl1/codemirror.css" type="text/css" media="screen" />
    <script src="http://code.jquery.com/jquery-1.10.2.min.js"></script>
    <script type="text/javascript" src="http://code.guru99.com/perl/perl.js"></script>
    <style>
    .CodeMirror {
    border: 1px solid #eee;
    }   
    .CodeMirror-scroll {
    height: auto;
    overflow-y: hidden;
    overflow-x: auto;
    }
</style>
<script>
$(document).ready(function(){
  $("form").submit(function(){
    alert("Submitted");
  });
});
</script>
<script type="text/javascript">

    function execute() {
            p5pkg.CORE.print = function(List__) {
                var i;
                for (i = 0; i < List__.length; i++) {
                  document.getElementById('print-result').value += p5str(List__[i])
                }
                return true;
            };
            p5pkg.CORE.warn = function(List__) {
                var i;
                List__.push("\n");
                for (i = 0; i < List__.length; i++) {
                    document.getElementById('log-result').value += p5str(List__[i]);
                }
                return true;
            };
            p5pkg["main"]["v_^O"] = "browser";
            p5pkg["main"]["Hash_INC"]["Perlito5/strict.pm"] = "Perlito5/strict.pm";
            p5pkg["main"]["Hash_INC"]["Perlito5/warnings.pm"] = "Perlito5/warnings.pm";

            var source = document.getElementById('source').value;
            alert(source);
            var pos = 0;
            var ast;
            var match;
            document.getElementById('log-result').value   = "";
        //  document.getElementById('js-result').value    = "";
            document.getElementById('print-result').value = "";
            try {
                // compile
                document.getElementById('log-result').value += "Compiling.\n";
                var start = new Date().getTime();
                var js_source = p5pkg["Perlito5"].compile_p5_to_js([source]);
                var end = new Date().getTime();
                var time = end - start;
                document.getElementById('log-result').value +=  "Compilation time: " + time + "ms\n";
        //      document.getElementById('js-result').value  += js_source + ";\n";

                // run
                start = new Date().getTime();
                eval(js_source);
                end = new Date().getTime();
                time = end - start;
                document.getElementById('log-result').value += "Running time: " + time + "ms\n";

                p5pkg.CORE.print(["\nDone.\n"]);
            }
            catch(err) {
                document.getElementById('log-result').value += "Error:\n";
                document.getElementById('log-result').value += err + "\n";
                document.getElementById('log-result').value += "Compilation aborted.\n";
                  }
        }
    </script>
    </head>
    <body>
    <form>
<textarea id="source" cols="70" rows="10">
say 'h';
</textarea>
    <div class="hint">This code is editable. Click Run to execute.</div>
    <input type="button" value="Run" onclick="execute()"/></br>
Output:</br>
    <textarea id="print-result" disabled="true" rows="10" cols="70"></textarea></br>
Log:</br>
    <textarea  id="log-result" disabled="true" cols="70"></textarea>
    <script>
      var editor = CodeMirror.fromTextArea(document.getElementById("source"), {
        lineNumbers: true,
        indentUnit: 4,
        indentWithTabs: true,
        enterMode: "keep",
        tabMode: "shift"
      });
    </script>
</form>
    </body>
</html>

So how can I get the current value of the textarea? Please help me guys.

Solution

I'm not familiar with CodeMirror, but what you exactly see on the screen, is not your original #source anymore. Instead there are several elements created by CodeMirror, and the original textarea is hidden.

When I look at the documentation, I found this:

var source = editor.doc.getValue();
alert(source);

Or, since you've constructed the editor object with fromTextArea() method, you can update the value of the the textarea before reading it:

editor.save();
var source = document.getElementById('source').value;           
alert(source);

Notice also what Adam has said about submitting the form. And there are invalid </br> tags in your HTML, the correct form is <br />.

Please visit at CodeMirror User Manual for the furher information.