SOURCE

var btn=document.getElementById('btn');
var n=10;
var timer=null;

function fun(){
    btn.disabled=true;
    btn.value = '请再阅读' + n + '秒！';
    n=n-1;
    timer=window.setTimeout(fun,1000);
    if(n==8){
        
        n=10;
        window.clearTimeout(timer);
        btn.disabled = false;
        btn.value = '注册';
    }
    
}

btn.onclick=fun;

<form id="form1" name="form1" method="post" action="">
  <label for="textfield"></label>
  <input name="textfield" type="button" id="btn" value="点击阅读后注册" />
</form>