function ChooseCom() { 
maxLength = 1000; 
M = window.document.book.message.value.length; 
window.document.book.msgCT.value = maxLength-M; 
if (M > maxLength) { 
window.document.book.message.value = window.document.book.message.value.substring(0,maxLength); 
window.document.book.msgCT.value = 0; } 
}