var secs = 10;
var wait = secs * 1000;
document.post_true.posta.value = "认真阅读 还有 " + secs + " 秒";
document.post_true.postb.value = "认真阅读 还有 " + secs + " 秒";

document.post_true.posta.disabled = true;
document.post_true.postb.disabled = true;

for(i = 1; i <= secs; i++) {
        window.setTimeout("update(" + i + ")", i * 1000);
}
window.setTimeout("timer()", wait);
function update(num, value) {
        if(num == (wait/1000)) {
                document.post_true.posta.value = "开始写信";
		document.post_true.postb.value = "开始写信";
        } else {
                printnr = (wait / 1000)-num;
                document.post_true.posta.value = "认真阅读 还有 " + printnr + " 秒";
		document.post_true.postb.value = "认真阅读 还有 " + printnr + " 秒";
        }
}
function timer() {
        document.post_true.posta.disabled = false;
	document.post_true.postb.disabled = false;
        document.post_true.posta.value = "开始写信";
        document.post_true.postb.value = "开始写信";
}