compileSvelteComponent.js

// packages
const rollup = require('rollup');
const svelte = require('rollup-plugin-svelte');
const { nodeResolve } = require('@rollup/plugin-node-resolve');
const sucrase = require('@rollup/plugin-sucrase');
const requireFromString = require('require-from-string');

const defaultInputOptions = {
	plugins: [
		svelte({ generate: 'ssr', hydratable: true }),
		nodeResolve(),
		sucrase({ transforms: ['typescript'] }),
	],
};

const outputOptions = { format: 'commonjs' };

async function compileSvelteComponent(input) {
	// prepare the bundle
	const bundle = await rollup.rollup({ input, ...defaultInputOptions });

	// generate our output
	const { output } = await bundle.generate(outputOptions);

	// we only care about our singular bundle and its code
	const code = output[0].code;

	// prep our rendered Component
	const Component = requireFromString(code);

	// it is ready
	return Component;
}

(async () => {
	// it's ready to go
	const HelloWorld = await compileSvelteComponent('HelloWorld.svelte');

	console.log(HelloWorld.render().html);
	console.log(HelloWorld.render({ name: 'Will' }).html);
})();

HelloWorld.svelte

<script>
  import Paragraph from "./Paragraph.svelte";
  export let name = "Abe";
</script>

<h1>Hello, {name}!</h1>
<Paragraph />

math.ts

export function square(n: number): number {
	return n * n;
}

package.json

{
  "private": true,
  "dependencies": {
    "@rollup/plugin-node-resolve": "^8.0.0",
    "@rollup/plugin-sucrase": "^3.0.2",
    "journalize": "^2.4.0",
    "require-from-string": "^2.0.2",
    "rollup": "^2.11.0",
    "rollup-plugin-svelte": "^5.2.2",
    "svelte": "^3.23.0"
  }
}

Paragraph.svelte

<script>
  import { intcomma } from "journalize";
  import { square } from "./math.ts";

  let n = 5;
</script>

<p>I am a paragraph! This is a number: {intcomma(5432)}</p>
<p>The number {n} squared is {square(n)}.</p>