本架图书.length报错

src/views/bookRackList.vue

@@ -25,7 +25,7 @@
         </div>
         <div class="rack-floor">
           <span :class="['icon','iconfont','icon-l'+index]" @click="handlePage(-1)">&#xe631;</span>
-          <p><span style="margin-right:25px">第{{ index+1 }}层</span><span>(共{{ bookList[item].length }}本)</span></p>
+          <p><span style="margin-right:25px">第{{ index+1 }}层</span><span>(共{{ bookList[item]?bookList[item].length:0 }}本)</span></p>
           <span :class="['icon','iconfont','icon-r'+index]" @click="handlePage(1)">&#xe62f;</span>
         </div>
       </div>