Make it compatible with Node's ESM imports.

[navaru]

Currently if I run a compiled svelte app in esm format on node for SSR I get the following error:

node --experimental-modules --experimental-json-modules --es-module-specifier-resolution=node svelte.app.mjs (node v14)

import { create_ssr_component } from 'svelte/internal';
         ^^^^^^^^^^^^^^^^^^^^
SyntaxError: The requested module 'svelte/internal' does not provide an export named 'create_ssr_component'

To fix that issue I added type: "module" to node_modules/svelte/package.json, but the svelte/compiler is compiled in umd format and throws an error:

import compiler from "svelte/compiler";
       ^^^^^^^^
SyntaxError: The requested module 'svelte/compiler' does not provide an export named 'default'

Can we change how svelte/compiler is built, to something similar to svelte/internal?

[AlbertMarashi]

Would adding
type: "module" break it for people below node 13?

[navaru]

Starting with Node v12 if the file ending is .js it will search for the nearest package.json and look for the "type": "module" field and load it as an ES module.

I could dig in to see how we can make it work, but I need to know if we can also change how the svelte/compiler is built.

[Pierstoval]

Not sure what to do, but there's also an issue when fetching the package via Pika, mostly when using Deno.

If I have code like this:

import compile from 'https://cdn.pika.dev/svelte@^3.23.0';

There is an issue when resolving files and types:

error: relative import path "svelte/internal" not prefixed with / or ./ or ../ Imported from "https://cdn.pika.dev/-/[email protected]/dist=es2019,mode=types/types/runtime/ambient.d.ts"

I tried to allow exporting the compiler to ESM via #4972 , and when I do this on my machine and import {compile} from './compiler.mjs';, it works as expected. Only the frontend-side module doesn't work yet because of the same svelte/internal issue, I don't know (yet) how to fix it.

[slightlyfaulty]

This is also an issue with Webpack 5. Because it now follows strict ESM import rules, you get a bunch of errors from Svelte imports like this:

ERROR in ../../node_modules/svelte/easing/index.mjs 1:0-49
Module not found: Error: Can't resolve '../internal' in '.../node_modules/svelte/easing'
Did you mean 'index.mjs'?
BREAKING CHANGE: The request '../internal' failed to resolve only because it was resolved as fully specified
(probably because the origin is a '*.mjs' file or a '*.js' file where the package.json contains '"type": "module"').
The extension in the request is mandatory for it to be fully specified.
Add the extension to the request.

Currently to get Svelte to work in Webpack 5 you have to completely disable strict ESM imports.

[dummdidumm]

Svelte provides the exports field now so this should be resolved.