pref(wasm): deduplicate web-worker code in browser.js

[privatenumber]

Problem

In the WASM distribution, a pretty large Web Worker function was being duplicated and creating bloat.

Changes

Reuse Web Worker code by leveraging toString().

File	Size before	Size after
lib/browser.js	122 KB	95 KB
lib/browser.min.js	50 KB	40KB
esm/browser.js	118 KB	93 KB
esm/browser.min.js	48 KB	39 KB

[evanw]

This used to be how esbuild works. However, it was deliberately changed because esbuild (and likely some other tools too) don't fully support code that uses Function.prototype.toString.

I recommend not using esbuild if you're worried about this level of bloat. This PR saves ~10 kb but the WebAssembly binary for esbuild is currently more than 10,000 kb, so this PR only reduces the size by about 0.1%.

[privatenumber]

This used to be how esbuild works. However, it was deliberately changed because esbuild (and likely some other tools too) don't fully support code that uses Function.prototype.toString.

Ah right. I wonder if it could be the other way around then? Keep it as a string, and run it through eval or new Function for the main thread version.

I recommend not using esbuild if you're worried about this level of bloat. This PR saves ~10 kb but the WebAssembly binary for esbuild is currently more than 10,000 kb, so this PR only reduces the size by about 0.1%.

It's true the total size savings are trivial. But in my usage, I'm bundling the JS part in the same chunk as my entry-point, and the WASM binary is loaded separately. So the reduction in the JS files had some notable impact.

[evanw]

That also used to be how esbuild works (using new Function to construct the worker function). However, that prevented people from using esbuild in environments where dynamic JavaScript evaluation is forbidden, such as Cloudflare Workers or Deno Deploy: #2081. So esbuild was changed to work the way it does now to enable these use cases.

[privatenumber]

Gotcha, sorry to make you revisit this problem. I underestimated how complex this is. I appreciate your patience in explaining this to me.

You may have already thought of this too, but what do you think of separating out the Web Worker/worker_threads versions into another file/entry-point?

"exports": {
	".": {
		"node": {
			"worker": "./lib/node/worker_threads.js",
			"default": "./lib/node/main.js"
		},
		"default": {
			"worker": "./lib/browser/web-worker.js",
			"default": "./lib/browser/main.js"
		}
	},
	"./main": {
		"node": "./lib/node/main.js"
		"default": "./lib/browser/main.js"
	},
	"./worker": {
		"node": "./lib/node/worker_threads.js"
		"default": "./lib/browser/web-worker.js"
	}
}
"