How to call pageBeforeUnmount when keepAlive enabled

Questions
1

I’ve read this doc page

routePage.html

<template>
<!-- ..... -->
</template>
<script>
return{
on:{
pageAfterIn:function(){
// called once, fine here
},
pageBeforeUnmount:function(){
// not called for one or more times
}
}
}
</script>

routes.js

var routes = [
  // ...
  {
    path: "/routePath/",
    componentUrl: "./pages/routePage.html",
    name: "routeName",
    keepAlive: true,
  },
// ...
];