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Limit a textarea to a maximum lengthTag(s): Form


First technique, you validate on the submit the textarea length and return false if too long. 
<SCRIPT LANGUAGE="JAVASCRIPT">
function checkLength(form){
    if (form.description.value.length > 20){
        alert("Text too long. Must be 20 characters or less");
        return false;
    }
    return true;
}
</SCRIPT>

<FORM ACTION="..." METHOD="..." onSubmit="return checkLength(this)">

Second technique, as you typed, the length is checked. If the input is too long then it is truncated. 

<script>
function limitText(limitField, limitNum) {
    if (limitField.value.length > limitNum) {
        limitField.value = limitField.value.substring(0, limitNum);
    } 
}
</script>

<form name="myform">
textarea limit 20 chars :<br>
<textarea rows="5" cols="30" onKeyDown="limitText(this,20);" 
onKeyUp="limitText(this,20);">
</textarea><br>
</form>
textarea limit 20 chars :

thanks to wsperry for the tip