How to max 250 character in textbox by javascript?

Html.TextAreaFor(model => model.SeoDescription, new { @class = "text", @style = "width:98%", @id = "SeoDesc", @maxlength = "250", onkeyup = "countSeoDesc(this);", @rows = "3" })
<p id="messageSeoDesc" class="text-right">[250 char]</p>

<script type="text/javascript">
    function countSeoDesc() {
        debugger;
        var area = document.getElementById("SeoDesc");
        var message = document.getElementById("messageSeoDesc");
        var maxLength = 250;
        if (area.value.length <= maxLength) {
            message.innerHTML = "[" + (maxLength - area.value.length) + " char" + "]";
        }
    }
</script>