Migration Path

[antony]

Opening this issue as a way of tracking a "migration guide" from Sapper to Kit.

One idea I've been thinking about is a package called @sveltejs/backport which you can install to "polyfill" methods/functions/behaviour/utilities which have been removed/renamed/signature-adusted. You can then strip out legacy over time, eventually uninstalling the package, rather than trying do delay until you have time to migrate larger apps.

This might be impossible though, but either way, we should have a living migration step list:

• Remove rollup.config.js or webpack.config.js. Add any custom config to vite.config.js
• Replace imports from @sapper/app to imports from... wherever we end up putting stuff ($app?)
• If you have src/node_modules/components, move it to src/components and update the import path to $components
• Move any custom server.js/client.js code to [TBD]
• Update endpoints (no more req/res)
• load (fka preload) (Implement load #272)
• render / prerender methods
• #svelte target element (provide element to render to - closes #154 #157).
• preloading / navigating store (stores.preloading -> stores.navigating #215)
• stores vs getStores (Consider renaming getStores back to stores #187)
• adapters and svelte-kit adapt (create separate svelte-kit adapt command #221)
• Svelte-specific prefix (Prefix SvelteKit-specific stuff #288)
• error and layout pages prefixed by $ instead of _

[Rich-Harris]

Edited the comment to make a start on the list