[adapter-cloudflare-workers] "Unexpected character '#'" error when running "wrangler publish"

[danawoodman]

Describe the bug
Using the CloudFlare Worker adapter with the latest Kit (1.0.0-next.89) and attempting to publish is causing an Unexpected character '#' error:

wrangler publish

up to date, audited 1 package in 137ms

found 0 vulnerabilities
👀  ./workers-site/index.js 3328:2
Module parse failed: Unexpected character '#' (3328:2)
You may need an appropriate loader to handle this file type.
| }
| var ReadOnlyFormData = class {
>   #map;
|   constructor(map) {
|     this.#map = map;

My wrangler.toml:

name = "kit-workers"
type = 'webpack'
account_id = '...'
route = ''
zone_id = ''
usage_model = ''
workers_dev = true
target_type = "webpack"
site = {bucket = "./build", entry-point = "workers-site"}

Logs

To Reproduce

npm init svelte@latest kit-workers
cd kit-workers
npm i -D @sveltejs/adapter-cloudflare-workers@next
# ... add adapter to svelte.config.cjs
wrangler init --site kit-workers
# ... add content to match above (e.g. add account_id and update bucket path)
npm run build
wrangler publish
# error occurs

Expected behavior
It to deploy to CF worker sites :)

Stacktraces
See top

Information about your SvelteKit Installation:

Diagnostics

• The output of npx envinfo --system --npmPackages svelte,@sveltejs/kit,vite --binaries --browsers:

  System:
    OS: macOS 11.2
    CPU: (8) arm64 Apple M1
    Memory: 217.56 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 15.12.0 - ~/.nvm/versions/node/v15.12.0/bin/node
    npm: 7.6.3 - ~/.nvm/versions/node/v15.12.0/bin/npm
  Browsers:
    Brave Browser: 89.1.22.71
    Chrome: 90.0.4430.85
    Safari: 14.0.3
  npmPackages:
    @sveltejs/kit: next => 1.0.0-next.89 
    svelte: ^3.29.0 => 3.37.0 
    vite: ^2.1.0 => 2.2.3 

• Your browser: Brave (not relevant)

• Your adapter: Cloudflare Workers

Severity
Blocking my usage of CF Workers with Kit but I'm just poking around, so not critical, more of an FYI

Additional context
Not that I can think of!

[CedricDumont]

a workarround untill fixed (or the fix) is to replace the code in node_modules/@sveltejs/adapter-cloudflare-workers/index.js the esbuild part (esbuild.build{....) with:

await esbuild.build({
				entryPoints: ['.svelte/cloudflare-workers/entry.js'],
				outfile: `${entrypoint}/index.js`,
				bundle: true,
				target: 'es2020',
				platform: 'node' // TODO would be great if we could generate ESM and use type = "javascript"
			});

(set the target to target: 'es2020') as #map is the translation to a private property and not supported by cloudflare at the moment...
I tested and it worked