تفضل اخي
كود بلغة HTML:
<html> <head> <script type="text/javascript">
function writing(TheText)
{
document.getElementById('mytext').value+=TheText
}
</script> </head> <body> <button onclick="writing('montadaphp')">Click</button> <textarea id="mytext" rows="5" cols="20"></textarea>.
</body> </html>