diff --git a/src/App.vue b/src/App.vue
index 223a7d4..e9655d9 100644
--- a/src/App.vue
+++ b/src/App.vue
@@ -132,7 +132,7 @@ export default {
             this.selectOffLineDevice()
           }
         } else {
-            let str1 = data.monitorId.slice(-10)
+            let str1 = String(data.monitorId).slice(-10)
             this.isOnline[str1] = new Date().getTime()
             this.selectOffLineDevice()
         }