uniapp+vant+vue2真机运行出现userAgent没有定义的错误

[suolong182]

Reproduction Link

https://gitee.com/suolong182/shop-h5.git

Vant Version

"vant": "^2.13.2"

Describe the Bug

使用若依的移动端框架+vant2+vue2+uniapp，在真机运行时会报错，报错如下： reportJSException >>>> exception function:createInstanceContext, exception:white screen cause create instanceContext failed,check js stack ->Uncaught TypeError: Cannot read property 'userAgent' of undefined at isIOS (app-service.js:14002:69) at (app-service.js:13970:31) at webpack_require (app-service.js:80:30) at (app-service.js:13377:20) at webpack_require (app-service.js:80:30) at (app-service.js:11488:37) at webpack_require (app-service.js:80:30) at (app-service.js:9268:43) at webpack_require (app-service.js:80:30) at eval (:11:36)

Reproduce Steps

Device / Browser

No response