svelte: Logical nullish/or (and other types of) assignment(s) doesn't work in Svelte

Describe the bug

Logical nullish assignment (as well as Logical OR assignment and other types of Logical assignments) doesn’t work in Svelte

Reproduction

https://svelte.dev/repl/e5054000ffb442ad85c4d7bbc821d8f5?version=3.42.1

Logs

unexpected token '??='
SyntaxError: Unexpected token '??='
    at new Function (<anonymous>)
    at instantiateModule (/mnt/sda1/Programovanie/test/node_modules/vite/dist/node/chunks/dep-c1a9de64.js:73464:9)

System Info

System:
    OS: Linux 5.11 Ubuntu 20.04.2 LTS (Focal Fossa)
    CPU: (8) x64 Intel(R) Core(TM) i5-8300H CPU @ 2.30GHz
    Memory: 216.20 MB / 15.46 GB
    Container: Yes
    Shell: 5.0.17 - /bin/bash
  Browsers:
    Chrome: 92.0.4515.131
    Firefox: 91.0

Severity

annoyance

About this issue

Original URL
State: closed
Created 3 years ago
Comments: 16 (16 by maintainers)

Most upvoted comments

I don’t think this is related to svelte-preprocess nor svelte-repl. Svelte should be able to parse logical assignments, and also track reactivity through it. Currently the former should only require an update to acorn, the latter however may need some changes to make sure it works.

bluwy on Aug 14, 2021

Oh, right, I had thought this was already working in Svelte. What you’re seeing in the REPL is just that its version of Rollup needs upgrading to support that syntax. There may be a PR for that already. In any case, this works in Svelte itself, and if you’re having issues with something unrelated, please pursue the usual avenues for support.

Conduitry on Aug 14, 2021

@benbender You’re right. Looks like Svelte’s acorn version is up-to-date and should support logical assignments. If this only happens in the REPL and not locally, it should be an issue for svelte-repl then, and I see you’ve opened an issue there: https://github.com/sveltejs/svelte-repl/issues/171

Though re that issue, I don’t think acorn needs to be updated to have this work, I’m guessing that it’s rollup that should be updated instead since acorn is only used in svelte-repl for converting cjs to esm, and Svelte components are already esm.

bluwy on Aug 14, 2021

The REPL is plain Svelte, so I don’t think there is a “real” bug either. It doesn’t (sadly and f.e.) doesn’t even support typescript at all… If you want to request additional features from the REPL, the repo to go is here: https://github.com/sveltejs/svelte-repl

benbender on Aug 14, 2021

@Mlocik97 Afaik this is expected. See https://github.com/sveltejs/svelte-preprocess#modern-javascript-syntax

benbender on Aug 14, 2021