Fixed flat not polyfilled error in vue cli3 (#4694)

CHANGELOG.md

@@ -23,6 +23,7 @@ ChangeLog
 - **Update:** Fixed `virtualScroll` option bug with treegrid extension.
 - **Update:** Fixed input keyboard bug for mobile extension.
 - **Update:** Fixed detail view column reorder bug for reorder-columns extension.
+- **Update:** Fixed `flat` not polyfilled error in vue cli3.
 - **Update:** Removed `resetWidth` method and use `resetView` instead.
 
 ### 1.15.5

src/utils/index.js

@@ -77,7 +77,7 @@ export default {
   },
 
   updateFieldGroup (columns) {
-    const allColumns = columns.flat()
+    const allColumns = [].concat(...columns)
 
     for (const c of columns) {
       for (const r of c) {