vue watch报错：Error in callback for watcher “xxx“: “TypeError: Cannot read properties of undefined ...(vue的watch不生效)

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vue watch报错：Error in callback for watcher “xxx“: “TypeError: Cannot read properties of undefined ...

一、问题

二、解决方法

三、总结

一、问题

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1.监听了一个data里面的对象竟然报错了，错误还奇奇怪怪的：不能在 undefined上使用 apply方法

1）详细错误如下：

vue.esm.js?9b69:5059 [Vue warn]: Error in callback for watcher "flowCategory": "TypeError: Cannot read properties of undefined (reading 'apply')"found in---> <FlowItem> at src/projects/comen/implemenceWorkstation/flowSetting/FlowItem.vue <ElTabPane> at packages/tabs/src/tab-pane.vue <ElTabs> at packages/tabs/src/tabs.vue <View> at src/views/implemenceWorkstation/flowSetting/view.vue <Index> at src/layout/index.vue <App> at src/App.vue <Root>warn$2 @ vue.esm.js?9b69:5059logError @ vue.esm.js?9b69:3728globalHandleError @ vue.esm.js?9b69:3724handleError @ vue.esm.js?9b69:3691invokeWithErrorHandling @ vue.esm.js?9b6

2）代码如下：

watch: { flowCategory: { hanlder(newval, oldval) { console.log('flowCategory', newval, oldval); }, deep: true } }二、解决方法

1.是不是看着上面的代码没问题，我也是很自信，不就是在handler函数中打印了变化前后的值吗？写法就是这样啊，我也是这样自信。

2.找了半天发现自己把 handler 这个单词写错了，敲错了写成'hanlder“了，ide也没有提示 &***&

改成下面这样就可以了

watch: { flowCategory: { handler(newval, oldval) { console.log('flowCategory', newval, oldval); }, deep: true } } vue watch报错：Error in callback for watcher “xxx“: “TypeError: Cannot read properties of undefined ...(vue的watch不生效)