ts-jest VS plugins

use ts-jest and set up Paths Re-Map

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.

ts-jest: A transformer for handling TypeScript files.

Thankfully using TypeScript and TypeScript project references makes the intricate problem of using Jest easier since we can make use of the excellent ts-jest Jest transformer. All we need to do it point ts-jest to the respective tsconfig.json file for each package (see example jest.config.js). Since we have configured TypeScript to be composite and incremental, we do not need to recompile TypeScript for dependencies of a package we want to test, which significantly reduces the runtime for unit tests. ts-jest will also ensure that any error message will reference the line numbers in the source TypeScript files.

We need to configure Jest to transform our files. We must explicitly set our test environment to jsdom, which we are using through Jest. Since v27 Jest's default test environment is node. I will put the configuration in a specific Jest configuration file called jest.config.json in the project root folder. If you create a configuration file called jest.config.js, Vite will complain as it expects only ESM JavaScript by default. Vite will recommend that you rename it to a ".cjs" file if you want to do it that way. You can look at the different ways to configure Jest if you are unsure about the file conventions. If you're using TypeScript, you need to configure svelte-preprocess and ts-jest also, see the svelte-jester docs for how to do that.

Next, we need to tell Rollup which of the modules used in our code are external to our library. Together with @rollup/plugin-node-resolve, this ensures that Rollup doesn't bundle those dependencies into our final bundle. The function makeExternalPredicate() generates the list of package names specified in dependencies and peerDependencies in package.json. All credit for this and a big thank you goes out to Mateusz Burzyński for providing it in this issue:

// If you have external dependencies installed from // npm, you'll most likely need these plugins. In // some cases you'll need additional configuration - // consult the documentation for details: // https://github.com/rollup/plugins/tree/master/packages/commonjs resolve({ browser: true, dedupe: ['svelte'], }), commonjs(), // In dev mode, call `npm run start` once // the bundle has been generated !production && serve(), // Watch the `public` directory and refresh the // browser on changes when not in production !production && livereload('public'), // If we're building for production (npm run build // instead of npm run dev), minify production && terser(), ], watch: { clearScreen: false, },

In Webpack 5, this is (surprisingly) simple to setup. Parcel 2 handles this out of the box with a special import prefix. Rollup has an official plugin.

The only workaround to have an isomorphic __dirname or __filename to be used for both "cjs" and "esm" without using build-time tools like @rollup/plugin-replace or esbuild "define" would be using a library like filedirname that does a trick inspecting error stacks, it's clearly not the cleanest solution.

import svelte from 'rollup-plugin-svelte'; import commonjs from '@rollup/plugin-commonjs'; import resolve from '@rollup/plugin-node-resolve'; import livereload from 'rollup-plugin-livereload'; import { terser } from 'rollup-plugin-terser'; import css from 'rollup-plugin-css-only'; import sveltePreprocess from 'svelte-preprocess'; const production = !process.env.ROLLUP_WATCH; function serve() { let server; function toExit() { if (server) server.kill(0); } return { writeBundle() { if (server) return; server = require('child_process').spawn( 'npm', ['run', 'start', '--', '--dev'], { stdio: ['ignore', 'inherit', 'inherit'], shell: true, } ); process.on('SIGTERM', toExit); process.on('exit', toExit); }, }; } export default { input: 'src/main.js', output: { sourcemap: true, format: 'iife', name: 'app', file: 'public/build/bundle.js', }, plugins: [ svelte({ preprocess: sveltePreprocess({ sourceMap: !production, postcss: { plugins: [require('tailwindcss'), require('autoprefixer')], }, }), compilerOptions: { // enable run-time checks when not in production dev: !production, }, }), // we'll extract any component CSS out into // a separate file - better for performance css({ output: 'bundle.css' }), // If you have external dependencies installed from // npm, you'll most likely need these plugins. In // some cases you'll need additional configuration - // consult the documentation for details: // https://github.com/rollup/plugins/tree/master/packages/commonjs resolve({ browser: true, dedupe: ['svelte'], }), commonjs(), // In dev mode, call `npm run start` once // the bundle has been generated !production && serve(), // Watch the `public` directory and refresh the // browser on changes when not in production !production && livereload('public'), // If we're building for production (npm run build // instead of npm run dev), minify production && terser(), ], watch: { clearScreen: false, }, };

Even for JSON files, rollup needs an aditional library - a json plugin. The installation & configuration will be covered below.

If I do the same steps with vite everything seems to work fine. What am I doing wrong? I have tried using the wasm package from rollup @rollup/plugin-wasm but have not been successful.

And then one Rollup plugin to integrate Babel:

@rollup/plugin-babel: Triggers the transpile step through Babel (basically what we have done by means of the babel-cli for the unbundled versions). As we are using babel only for the bundled artifacts babelHelpers are set to bundled, so in case any helpers are needed these are added to the bundle file (you can read more about the property in the documentation). In include and extensions the files and their extensions (ts/js for the example library) to process are defined, whereasexcludes indicates folders/patterns which should be skipped (just the node_modules folder for the example library).

In case you're planning to build a SPA project(Single Page Application), you can use the createSpaConfig in Rollup configuration. Also, you can install the @rollup/plugin-typescript for seamless integration between Rollup and TypeScript.