JavaScript獲取輸入框內容

 <div class="fk_ban fk_ban1" style="width: 25%;margin: 10px 0;line-height:auto">買多少：</div>

                                    <div style="width: 70%;float: left;margin: 10px 0;word-break: break-all">
                                       <input type="text" name="buy_num" id="buy_name" >
                                    </div>
 <div style="width: 100%;float: left">
                                        <div style="width: 80px;float: left;margin-left: 60px;line-height: 30px;text-align: center;background: #84d1f2;color: #fff;margin-top: 20px;cursor: pointer"  <if condition="$item.status eq 0 ">onclick="buythis({$item.id},{$wayid})" </if>>
                                        <if condition="$item.status eq 0 ">購買</if><if condition="$item.status eq 1">出售中</if>
                                    </div>
  function buythis(id,wayid){

                var input = document.getElementsByName('buy_num')[0];
                // 獲取輸入框中的數據
                buyvalue  =input.value
                $("#buy_price").hide();
                confirm1("確定要進行購買嗎？","{:U('User/marketbuy')}"+"&id="+id+"&wayid="+wayid);
            }