Starter template for Sapper apps
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Update package.json with latest npm-run-all with event-stream fix
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The default Sapper template. To clone it and get started:

npx degit sveltejs/sapper-template my-app
cd my-app
npm install # or yarn!
npm run dev

Open up localhost:3000 and start clicking around.

Consult for help getting started.

Click here for the Rollup version of this template


Sapper expects to find three directories in the root of your project — app, assets and routes.


The app directory contains the entry points for your app — client.js, server.js and (optionally) a service-worker.js — along with a template.html file.


The assets directory contains any static assets that should be available. These are served using sirv.

In your service-worker.js file, you can import these as assets from the generated manifest...

import { assets } from './manifest/service-worker.js'; that you can cache them (though you can choose not to, for example if you don't want to cache very large files).


This is the heart of your Sapper app. There are two kinds of routes — pages, and server routes.

Pages are Svelte components written in .html files. When a user first visits the application, they will be served a server-rendered version of the route in question, plus some JavaScript that 'hydrates' the page and initialises a client-side router. From that point forward, navigating to other pages is handled entirely on the client for a fast, app-like feel. (Sapper will preload and cache the code for these subsequent pages, so that navigation is instantaneous.)

Server routes are modules written in .js files, that export functions corresponding to HTTP methods. Each function receives Express request and response objects as arguments, plus a next function. This is useful for creating a JSON API, for example.

There are three simple rules for naming the files that define your routes:

  • A file called routes/about.html corresponds to the /about route. A file called routes/blog/[slug].html corresponds to the /blog/:slug route, in which case params.slug is available to the route
  • The file routes/index.html (or routes/index.js) corresponds to the root of your app. routes/about/index.html is treated the same as routes/about.html.
  • Files and directories with a leading underscore do not create routes. This allows you to colocate helper modules and components with the routes that depend on them — for example you could have a file called routes/_helpers/datetime.js and it would not create a /_helpers/datetime route

Webpack config

Sapper uses webpack to provide code-splitting, dynamic imports and hot module reloading, as well as compiling your Svelte components. As long as you don't do anything daft, you can edit the configuration files to add whatever loaders and plugins you'd like.

Production mode and deployment

To start a production version of your app, run npm run build && npm start. This will disable hot module replacement, and activate the appropriate webpack plugins.

You can deploy your application to any environment that supports Node 8 or above. As an example, to deploy to Now, run these commands:

npm install -g now

Using external components

When using Svelte components installed from npm, such as @sveltejs/svelte-virtual-list, Svelte needs the original component source (rather than any precompiled JavaScript that ships with the component). This allows the component to be rendered server-side, and also keeps your client-side app smaller.

Because of that, it's essential that webpack doesn't treat the package as an external dependency. You can either modify the externals option in webpack/server.config.js, or simply install the package to devDependencies rather than dependencies, which will cause it to get bundled (and therefore compiled) with your app:

yarn add -D @sveltejs/svelte-virtual-list

Bugs and feedback

Sapper is in early development, and may have the odd rough edge here and there. Please be vocal over on the Sapper issue tracker.