Count how many characters in Text Area in HTML code

In HTML code
<form name="count_form" method="post" action="">
<textarea name="desc" cols="40" rows="7" id="desc"
    onKeyDown="CountWordsLeft(count_form, document.count_form.desc, document.count_form.count,100);"
    onKeyUp="CountWordsLeft(count_form, document.count_form.desc, document.count_form.count,100);"
    onPaste="CountWordsLeft(count_form, document.count_form.desc, document.count_form.count,100);">
</textarea>
<input readonly name="count" type="text" size="5" value="100">
</form>


--- In Javascript

function CountWordsLeft(myForm, field, count, no_words) {
    var text=field.value + " ";
    if(no_words>0)
    {
        var iwhitespace = /^[^A-Za-z0-9]+/gi; // remove initial whitespace
        var left_trimmedStr = text.replace(iwhitespace, "");
        var na = rExp = /[^A-Za-z0-9]+/gi; // non alphanumeric characters
        var cleanedStr = left_trimmedStr.replace(na, " ");
        var splitString = cleanedStr.split(" ");
        var word_count = splitString.length -1;
        count.value=no_words-word_count;
    }
}