类型错误：无法读取未定义的属性"长度"(React，heroku)

Question

react_devtools_backend.js:2574 TypeError: Cannot read property 'length' of undefined
at ra (react-dom.production.min.js:156)
at ba (react-dom.production.min.js:167)
at Object.wa [as useEffect] (react-dom.production.min.js:167)
at Object.t.useEffect (react.production.min.js:22)
at hn (makeStyles.js:191)
at p (makeStyles.js:228)
at withStyles.js:55
at oa (react-dom.production.min.js:157)
at La (react-dom.production.min.js:176)
at Vs (react-dom.production.min.js:271)

如何解决此错误?我使用react build pack在Heroku上托管了我的react应用程序，当我尝试加载一些使API调用的页面时，它显示了这个错误，但是当我在本地机器上运行它时，它运行得很好。

下面是我的代码片段，我认为它不会导致错误

{ 
!this.props.loading ? this.props.packs && 
this.props.packs?.length > 0 && this.props.packs?.map((pack) => 
{ return <Pack key={pack.id} 
pack={pack} onPurchasePackage={this.onPurchasePackage}/> }) : null
}

Answer 1

我发现了我的代码的问题。问题是我临时放置素材的方式。

export default connect(mapStateToProps, mapDispatchToProps)(withStyles(useStyles)(withErrorHandler(Packages, axios)));

export default connect(mapStateToProps, mapDispatchToProps)
(withStyles(styles, { withTheme: true })(withErrorHandler(Packages, axios)));