textarea byte check

function textAreaLengthCheck(thisObj, maxLengthByte) {
	var tempByteLength = 0, cutByteLength = 0; 
	for(var i = 0; i < thisObj.value.length; i++) { 
		if(escape(thisObj.value.charAt(i)).length > 4) { 
			tempByteLength += 2;
		} else {
			tempByteLength++; 
		} 



		if(tempByteLength < maxLengthByte) { 
			cutByteLength++; 
		}
	} 
	if(tempByteLength > maxLengthByte) { 
		alert("max byte : " + maxLengthByte);
		thisObj.value = thisObj.value.substring(0, (cutByteLength%2==1)?cutByteLength:cutByteLength+1); 
	} 

}

<textarea onkeyup="textAreaLengthCheck(this, 10)" name="test"></textarea>
ex.