ts-jest VS svelte-preprocess

Argument of type X is not assignable to parameter of type 'never' #2610

First, you can't use jest right out of the box, becuase Jest does not support ECMA script nor Typescript. For that, you need to use another dependency like ts-jest, which is a wrapper of jest itself. And maybe even a Babel preset if I need it to work with Babel.. Let's see what we have to do to get this to work.

use ts-jest and set up Paths Re-Map

Jest's out of the box config for TS doesn't do any type checking. You can integrate https://kulshekhar.github.io/ts-jest/ or you can call ‘tsc’ yourself separately

ts-jest has had some strange performance issues and workarounds in the past, though I haven’t used it very recently so it might have fixed those by now.

Since we're working with TypeScript, we can use ts-jest, which conveniently brings Jest along for the ride:

I want to save you from manually copying the snippets one by one, so here is a Gist with the complete test file. This can be easily executed with Jest (or ts-jest for TypeScript).

See the Jest configuration docs to learn more about Jest configuration. ts-jest also has good documentation.

Using @swc/jest to compile code to CommonJS is much faster than babel-jest, ts-jest which have long cold starts when executing tests in a large project.

You can learn more about the official svelte-preprocess and other available config here

svelte-preprocess is responsible for processing things like TypeScript and SCSS. The svelte compiler itself is only responsible for turning the svelte file into JavaScript.

svelte-preprocess should handle scss out-of-the-box, and it’s included in SvelteKit by default if you created your project with create-svelte

// svelte.config.js import sveltePreprocess from 'svelte-preprocess' export default { // Consult https://github.com/sveltejs/svelte-preprocess // for more information about preprocessors // **here -> postcss: true** preprocess: sveltePreprocess({ postcss: true, }) }

/** @type {import('@sveltejs/kit').Config} */ const config = { // Consult https://github.com/sveltejs/svelte-preprocess // for more information about preprocessors preprocess: preprocess({ typescript: true, postcss: true, scss: { prependData: @import 'src/styles/helpers/functions.scss'; } }), kit: { paths: { assets: '', base: dev ? '' : '/route/in/website' }, trailingSlash: 'always', adapter: adapter({ pages: 'build', assets: 'build', fallback: 'index.html' }), files: { hooks: 'src/hooks', }, prerender: { default: true, }, } };

Continue to use tags

In svelte.config.js ... (import aliases can be whatever you want)

1. import svelte_preprocess from 'svelte-preprocess'
2. import autoprefixer from 'autoprefixer'
3. pass the Svelte preprocessor to Kit's preprocess config option and pass the postcss plugin to that Svelte preprocessor:

svelte.config.js

import svelte_proprocess from 'svelte-process'
import autoprefixer from 'autoprefixer'

const config = {
    // Consult https://github.com/sveltejs/svelte-preprocess for more info
    preprocess: [
        svelte_preprocess({
            postcss: {
                plugins: [autoprefixer()]
            }
        })
    ]
}

import adapter from '@sveltejs/adapter-auto'; import preprocess from 'svelte-preprocess'; import { mdsvex } from 'mdsvex'; import remarkMath from 'remark-math'; import rehypeKatex from 'rehype-katex-svelte'; /** @type {import('@sveltejs/kit').Config} */ const config = { extensions: ['.svelte', '.svx', '.md'], // Consult https://github.com/sveltejs/svelte-preprocess // for more information about preprocessors preprocess: [ preprocess(), mdsvex({ extensions: ['.svx', '.md'], smartypants: true, layout: { project: "./src/routes/projects/layout.svelte", post: "./src/routes/blog/layout.svelte", }, remarkPlugins: [remarkMath], rehypePlugins: [rehypeKatex], }), ], kit: { adapter: adapter({ edge: false, external: [], split: false }) } }; export default config;

Have you tried https://github.com/sveltejs/svelte-preprocess

// We have changed the adapter line to use adapter-node@next import adapter from '@sveltejs/adapter-node@next'; import preprocess from 'svelte-preprocess'; /** @type {import('@sveltejs/kit').Config} */ const config = { // Consult https://github.com/sveltejs/svelte-preprocess // for more information about preprocessors preprocess: preprocess(), kit: { // We have changed this to point to a build directory adapter: adapter({ out: 'build' }) } }; export default config;