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0.0.54 • Public • Published

Sapper Site Generator

a very experimental static site generator overlay on top of Sapper.

Because Sapper needs fixes to support static export at scale, and moves too slowly for the development of this project, we use a light fork of Sapper ( instead of sapper itself. Hopefully this fork will not be necessary in future, but for now we need these fixes for ssg to work. We aim to keep this fork a superset of sapper as much as possible.

Example usage

Active Codebases you can see this project in use:

In v0.x we reserve the right to break APIs without warning. Get involved if you need advance warning.


yarn add ssg

Svelte and @ssgjs/sapper are included as direct dependencies, however feel free to also install them if you need to.


This project needs feedback and maintainers. In fact if you'd like to take it over please be my guest. I don't have time for this. I'm only doing it cause no one else has.

This is a very nascent project, you'll run into bugs. report them please and also help add tests. If you have feature suggestions please open an issue first to see if it is something we want, before wasting time on a PR.

Usage and CLI API

  • ssg eject - scaffold out fallback files used by ssg
  • ssg dev - same as sapper dev, runs data pipeline specified in ssg.config.js and watches those files
  • ssg export - same as sapper export, runs data pipeline specified in ssg.config.js and exports the sapper app as a static site.

Zero Config

By default, ssg works as a simple zero config layer over sapper. In fact, for the time being, ssg will endeavor to be a sapper superset as far as possible. It uses the programmatic api behind the cli commands, adding some functionality in the @ssgjs/sapper fork of sapper.

Fallbacks and ssg eject

ssg makes these Sapper files optional:

  • src/client.js
  • src/server.js
  • src/service-workers.js
  • src/template.html
  • rollup.config.js

They are located in the ejectableFiles folder.

However, you can scaffold out these files with the ssg eject command:

$ yarn ssg eject
✔ Pick files to copy out · template.html, client.js
✔ A file exists at src/template.html. Are you sure you want to overwrite? (y/N) · false
✔ A file exists at src/client.js. Are you sure you want to overwrite? (y/N) · true
copied /Users/swyx/Work/community/node_modules/ssg/ejectableFiles/client.js to src/client.js

Generating pages from data

  1. if you need to get data, you will have a src/routes/data/[ssgData].json.js file in your main Sapper project, that looks like this:
// src/routes/data/[ssgData].json.js`
const { getDataSlice, getIndex } = require('ssg/readConfig')
export async function get(req, res) {
  const { ssgData } = req.params
  const splitSlug = ssgData.split('___ssg___')
  const key = splitSlug[0]
  const uid = splitSlug[1]
  const mainIndex = getIndex()
  let data
  // console.log('getting', key, uid)
  if (uid === 'index') {
    data = mainIndex[key]
  } else {
    data = await getDataSlice(key, uid)
  if (typeof data !== 'undefined') {
    res.writeHead(200, { 'Content-Type': 'application/json' })
  } else {
    res.writeHead(404, { 'Content-Type': 'application/json' })
    res.end(JSON.stringify({ message: `Not found` }))

⚠️ STOP! the filename is extremely important! doublecheck it is src/routes/data/[ssgData].json.js or expect the above code to break

You can scaffold this file with ssg eject.

  1. If you need to send data, you should have a ssg.config.js that exports a createIndex (run once) and getDataSlice (run each time) function that provides this data:
// optional. called repeatedly, can be expensive
exports.getDataSlice = async (key, uid) => {
  console.log('optional getDataSlice action')
  // we dont really use the key here
  if (key === 'posts') {
    if (uid === 'foo') {
      return { title: 'foo', html: '<div> the foo post </div>' }
    } else {
      return { title: 'bar', html: '<div> the bar post </div>' }
  } else {
    throw new Error('invalid key ' + key )
exports.createIndex = async (mainIndex = {}) => {
  // do expensive initial fetches and cache them in .ssg/data.json
  mainIndex.index = [{ title: 'foo', slug: 'foo' }, { title: 'bar', slug: 'bar' }]
  return mainIndex
// optional lifecycle hook
exports.postExport = async mainIndex => {
  // eg for RSS
  console.log('postExport', mainIndex)

In your templates, you may now query this data at any time:

<!-- src/routes/talks/[slug].svelte -->
<script context="module">
  export async function preload({ params, query }) {
    cosnt key = 'posts'
    const res = await this.ssgData({ key, id: params.slug }) // defaults to key: 'ssgCoreData' and id: 'index'
    if (res.status === 200) {
      return data
    } else {
      this.error(res.status, data.message)
  export let data

When we drop Sapper we'll likely have a more ergonomic api for this.

Core Data

As of v0.45 ssg now also reads all markdown files in the root directory by default. This is inline with 11ty's practice and is configurable by setting a coreDataDirPath string in ssg.config.js:

// example ssg.config.js
exports.coreDataOpts = {
  coreDataDirPath: 'content/blog' // defaults to '.'

ssg dev

Under the hood, ssg runs sapper dev for you, and watches and reloads it whenever you change your config or contents folder.

It runs createIndex once and saves that result to a cache, and then you can run getDataSlice anytime you want to query that cache.


You can also use plugins that have prewritten createIndex and getDataSlice for you:

// ssg.config.js
const remark = require('@ssgjs/source-remark')
const writing = remark({ dirPath: 'content/writing' })
const speaking = remark({ dirPath: 'content/talks' })
// optional data plugins. must be object, so we can namespace
exports.plugins = {


You can run ssg export to export just like sapper export does. for convenience, I've included a netlify.toml config so you dont have to look it up. Just ssg eject.


ssg uses debug to log diagnostic messages. Set a Node env variable to enable this logging:

DEBUG=ssg ssg dev
# or DEBUG=* ssg export 

You have a few more degrees of control available incl filtering out messages, look at the debug docs for more ideas.


npm i ssg

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