What is the proper way to have an isBrowser/isNode check that causes the code to only bundle one of two paths depending on platform target?

[MicahZoltu]

const inBrowser = (typeof window !== "undefined");
let NodeWorker;
let NodeCrypto;
if (!inBrowser) {
    NodeWorker = require("worker_threads").Worker;
    NodeCrypto = require("crypto");
}

This code will fail to bundle when --platform=browser is set because neither of those libraries are available in the browser. How can I modify the isBrowser check such that esbuild will correctly skip those lines?

[hyrious]

You can add a try-catch around the requires so that esbuild won't check inside:

const inBrowser = (typeof window !== "undefined");
let NodeWorker;
let NodeCrypto;
if (!inBrowser) {
	try {
		NodeWorker = require("worker_threads").Worker;
		NodeCrypto = require("crypto");
	} catch {}
}

[MicahZoltu]

If in node, you would want an error if either of those fails. Adding a try with an empty catch would introduce a potential bug.

[MicahZoltu]

Hmm, this seems to do the trick. Why is it that esbuild ignores the contents of try/catch blocks?

const inBrowser = (typeof window !== "undefined");
let NodeWorker;
let NodeCrypto;
if (!inBrowser) {
    try {
        NodeWorker = require("worker_threads").Worker;
        NodeCrypto = require("crypto");
    } catch (error) {
        // necessary so esbuild ignores this
        throw error
    }
}

[hyrious]

esbuild reports that error because it can not bundle something not exist if that thing isn't externalized. But there's a common code pattern which gracefully handles "optional dependencies" (i.e. inside a try-catch block) so esbuild also allows that to swallow the error.

esbuild/internal/ast/ast.go

Lines 115 to 125 in 9eca464

	// True for the following cases:
	//
	// try { require('x') } catch { handle }
	// try { await import('x') } catch { handle }
	// try { require.resolve('x') } catch { handle }
	// import('x').catch(handle)
	// import('x').then(_, handle)
	//
	// In these cases we shouldn't generate an error if the path could not be
	// resolved.
	HandlesImportErrors

Other choices are that you can tell esbuild those node modules are externalized, or replaced with undefined:

• --external:worker_threads --external:crypto (example)
• Put this in your pakcage.json:

  "browser": { "crypto": false }

  (example)

[MicahZoltu]

Is it possible to achieve the second solution (just put undefined) via CLI options, or do I have to modify the package.json to achieve that?