SOURCE

function createOrder()
{
coffee=document.forms[0].coffee
txt=""
for (i=0;i<coffee.length;++ i)
{
if (coffee[i].checked)
{
txt=txt + coffee[i].value + " "
}
}
document.getElementById("order").value="您订购的咖啡带有： " + txt
}

<p>你喜欢怎么喝咖啡？</p> 
 <form> 
  <input type="checkbox" name="coffee" value="奶油">加奶油
  <br> 
  <input type="checkbox" name="coffee" value="糖块">加糖块
  <br> 
  <br> 
  <input type="button" onclick="createOrder()" value="发送订单"> 
  <br>
  <br> 
  <input type="text" id="order" size="50"> 
 </form>