How do I add a counter to a javascript text area that counts like Twitter but instead of down it goes up to a maximum of 150 characters
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I know little about javascript and implementing it but I found this:


    <script language="javascript" type="text/javascript">
    function limitText(limitField, limitCount, limitNum) {
    	if (limitField.value.length > limitNum) {
    		limitField.value = limitField.value.substring(0, limitNum);
    	} else {
    		limitCount.value = limitNum - limitField.value.length;
    	}
    }
    </script>

and then this piece to implement it:

    <form name="myform">
    <textarea name="limitedtextarea" onKeyDown="limitText(this.form.limitedtextarea,this.form.countdown,100);" 
    onKeyUp="limitText(this.form.limitedtextarea,this.form.countdown,100);">
    </textarea><br>
    <font size="1">(Maximum characters: 100)<br>
    You have <input readonly type="text" name="countdown" size="3" value="100"> character left.</font>
    </form>

How do I make it instead of it counting down but to count up to 150 characters?