ASP.NETでボタン二度押し禁止方法

var send = true;
function sendCheck() {
if(send) {
return false;
} else {
send = true;
return true;
}
}

document.onreadystatechange = function() {
if (document.readyState == 'interactive') {
send = false;
}
if (document.readyState == 'complete') {
send = false;
}
}