value.length < 10 return false not working

I was using a condition onsubmit to return false if the text field didn't have more than 10 characters however it stopped submitting at all just now, I don't think I changed anything less the condition but obviously I must 开发者_StackOverflow中文版have done something.

<form class="form-new" action="insert/insert.php" method="post" onsubmit="if (document.getElementById('post-input').value.length < 10) return false;">
    <textarea class="form-new" id="post-input" name="text"></textarea><br/>
    <input type="hidden" name="ciudad" value="<?=$city;?>">
    <input type="text" name="colegio" value="<?=$group;?>">
    <input class="form-new" type="submit" value="Publicar"/>
</form>

Is there a way round? Or am I just doing it wrong? Thanks

Here is your example.

But have a look, if you return false in onsubmit the form will be sent anyway. In order to perform alert or something like that, you should do something like this:

<script type="text/javascript">
    function checkLength() {
        var textarea=document.getElementById('post-input');
    alert(textarea.value.length >= 10);
        if (textarea.value.length >= 10) {
            document.getElementById('myform').submit();
        }
    }
</script>

<form class="form-new" action="insert/insert.php" id="myform" method="post">
    <textarea class="form-new" id="post-input" name="text"></textarea><br/>
    <input type="hidden" name="ciudad" value="<?=$city;?>">
    <input type="text" name="colegio" value="<?=$group;?>">
    <input class="form-new" type="button" value="Publicar" onclick="checkLength()"/>
</form>

and this is the link: http://jsfiddle.net/YNcU4/1/.

UPDATE: Please read comments. The original code should work.