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RFC: Saber Functions

functions folder

Functions are used to fetch data that you can inject to pages at build time, let's say you have a posts.js inside functions folder:

exports.handler = async ({ type }) => {
  const posts = await getAllPostsFromApi()
  return posts.filter(post => post.type === type)
}

<small>Since we need to get the return value before running webpack, you can only write JavaScript with features supported by your system's Node version.</small>

Then a function called posts will be available and you can use it like this in a page:

<script>
export const config = {
  injectProps: {
    drafts: {
      function: 'posts',
      options: {
        type: 'draft'
      }
    }
  }
}

export default {
  props: ['drafts']
}
</script>

By using injectProps here Saber will call the function at build time and inline result in your JavaScript bundle.

Pagination

We can create pagination based on injected props:

<script>
export const config = {
  paginate: {
    prop: 'drafts',
    perPage: 30
  },

  injectProps: {
    drafts: {
      function: 'posts',
      options: {
        type: 'draft'
      }
    }
  }
}

export default {
  props: ['drafts']
}
</script>

Exporting function

A function can be exported as a page just like a normal page, only thing you need to do is setting config.export option to true:

// functions/atom.xml.js
const getPosts = require('../get-posts')

exports.handler = async () => {
  const posts = await getPosts({ type: 'public' })
  const xml = generateXMLFeed(posts)
  return xml
}

exports.config = {
  export: true
}

When export is true, Saber automatically infers the actual link from its filename, in this case it would be /atom.xml. You can also set it to a string to use whatever permalink you want, e.g. /subscribe/rss.xml.

When export is true, the function's argument would be undefined unless you use dynamic parameter in its filename, for example functions/pages/[slug].json.js:

exports.handler = ({ slug }) => {
  return getPageBySlug(slug)
}

exports.config = {
  export: true
}

exports.getStaticPaths = () => {
  return [
    { slug: 'hello-world' },
    { slug: 'another-page' }
  ]
}

Because the path is dynamic you also need getStaticPaths to define a list of paths that need to be rendered at build time.

Now when you visit /pages/hello-world.json, then function argument will be { slug: 'hello-world' }

Adding a function from plugins

saber.functions.add(FunctionObject)