Access global computed properties in <script> tag - vue.js

Question

Vuepress defines some global properties than can be used in templates, like $page or $site.
https://github.com/vuejs/vuepress/blob/master/packages/docs/docs/guide/global-computed.md
I can use these within the <template> node, but trying to use them within <script> throws an error.
<template>
<div class="page">
<div class="content">
<div>{{ $page.frontmatter.description }} Works fine</div>
<div>{{ $frontmatter.description }} Does not work despite what's in docs</div>
<div>{{ description }} Doesn't work</div>
</div>
</div>
</template>
<script>
export default {
data() {
return {
description: this.$page.frontmatter.description, //not defined
description2: $page.frontmatter.description, //nor this
};
},
};
</script>

Answer 1

Your problem is not about using Vuepress Global Computed Properties inside <script> tag, it's actually about using Vuejs Computed Properties inside data().
If you simply create a Vue component like the code snippet below, you will find the variable testMessage is not defined either.
<template>
<div>{{ testMessage }}</div>
</template>
<script>
export default {
data() {
return {
testMessage: this.test
}
},
computed: {
test: function() {
return 'This is a test';
}
}
}
</script>
I don't know the exact reason for this, but I believe it's about the lifecycle of Vue instance. So I suggest you simply access the Global Computed Properties inside computed properties or methods:
<template>
<div>{{ description }}</div>
</template>
<script>
export default {
computed: {
description : function() {
return this.$page.frontmatter.description;
}
}
}
</script>