fix: isPlainObject incorrectly identifies objects wrapped in a Proxy object in Safari 10 (#1378) (#1379)

Author: reed-soul

packages/shared/src/utils.ts

@@ -151,8 +151,11 @@ export const objectToString = Object.prototype.toString
 export const toTypeString = (value: unknown): string =>
   objectToString.call(value)
 
-export const isPlainObject = (val: unknown): val is object =>
-  toTypeString(val) === '[object Object]'
+export const isPlainObject = (val: unknown): val is object => {
+  if (!isObject(val)) return false
+  const proto = Object.getPrototypeOf(val)
+  return proto === null || proto.constructor === Object
+}
 
 // for converting list and named values to displayed strings.
 export const toDisplayString = (val: unknown): string => {