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Tomasz Wegrzanowski
Tomasz Wegrzanowski

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Open Source Adventures: Episode 53: Setting up JSON imports for a Svelte project

In previous episode I created data export for BATTLETECH weapons data. Before I get to writing the app, I need to import the data.


First, we need to get through some rollup hell, as by default importing JSON does not work.

First we need to npm install --save-dev rollup-plugin-json, here's the resulting package.json:

  "name": "svelte-app",
  "version": "1.0.0",
  "private": true,
  "scripts": {
    "build": "rollup -c",
    "dev": "rollup -c -w",
    "start": "sirv public --no-clear"
  "devDependencies": {
    "@rollup/plugin-commonjs": "^17.0.0",
    "@rollup/plugin-node-resolve": "^11.0.0",
    "rollup-plugin-css-only": "^3.1.0",
    "rollup-plugin-json": "^4.0.0",
    "rollup-plugin-livereload": "^2.0.0",
    "rollup-plugin-svelte": "^7.0.0",
    "rollup-plugin-terser": "^7.0.0",
    "rollup": "^2.3.4",
    "svelte": "^3.0.0"
  "dependencies": {
    "sirv-cli": "^2.0.0"
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Then we need to import rollup-plugin-json and then add json() to list of plugins. It's a shame that JavaScript doesn't just work out of the box without stupid bundler configs, but that's the sad world we live in.

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 json from 'rollup-plugin-json'

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: [
      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:
      browser: true,
      dedupe: ['svelte']

    // 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
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After that we can verify that it imported the data correctly:

  import data from "./data.json"

<h1>Weapons Data</h1>

  {#each data as row}
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Story so far

All the code is on GitHub.

Coming next

Now that data import worked, in the next few episodes I'll create a small Svelte interactive visualization of the BATTLETECH weapons data.

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