[!] Error: UMD and IIFE output formats are not supported for code-splitting builds. Error: UMD and IIFE output formats are not supported for code-splitting builds.

I’m getting this when I build:

[!] Error: UMD and IIFE output formats are not supported for code-splitting builds.
Error: UMD and IIFE output formats are not supported for code-splitting builds.

yarn run v1.21.1
warning package.json: No license field
$ run-s build start
warning package.json: No license field
$ rollup -c

src/main.js → public/build/bundle.js...
(!) `this` has been rewritten to `undefined`
https://rollupjs.org/guide/en/#error-this-is-undefined
node_modules/intl-messageformat/lib/core.js
4: See the accompanying LICENSE file for terms.
5: */
6: var __assign = (this && this.__assign) || function () {
                   ^
7:     __assign = Object.assign || function(t) {
8:         for (var s, i = 1, n = arguments.length; i < n; i++) {
...and 1 other occurrence
node_modules/intl-messageformat/lib/formatters.js
1: var __extends = (this && this.__extends) || (function () {
                    ^
2:     var extendStatics = function (d, b) {
3:         extendStatics = Object.setPrototypeOf ||
...and 3 other occurrences
node_modules/intl-format-cache/lib/index.js
4: See the accompanying LICENSE file for terms.
5: */
6: var __spreadArrays = (this && this.__spreadArrays) || function () {
                         ^
7:     for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
8:     for (var r = Array(s), k = 0, i = 0; i < il; i++)
...and 1 other occurrence

...and 3 other files```

[timohausmann]

I’m also getting this error following instructions from the docs:

register('en', () => import('./en.json'));

I found these solutions:

• fallback to addMessages instead of register
• add output: { inlineDynamicImports : true } to your rollup.config.js
• put i18n-files in /public and code your own funny little Promise loader like:

register('en', function() {
    return window.fetch('/i18n/en.json')
        .then(data => data.json())
        .catch(error => console.log('i18n fetch error', error))
});

I don’t wanna be a nagging b*tch but in my opinion this is a valid issue with this package (or rather it docs) if it doesn’t provide an easy out-of-the-box solution that works with the very default Svelte+Rollup installation but requires a deep understanding of Rollup configs. If you let me know what’s your go-to solution for dynamic imports with Svelte+Rollup I’ll happily provide a PR for the docs.

[kaisermann]

@timohausmann You’re totally right! I should make it clearer the scenario where one can use dynamic imports or not. The lib was made with mostly Sapper in mind, which has built-in support for dynamic imports. A PR would be great! We could add a section in the FAQ and some note in the getting started document.