Dynamic import to CommonJS does not compile to require

[lxsmnsyc]

There seems to be a regression that happened between 0.9.5 and 0.12.22.

When bundling ESM code to Node(platform: "node" and format: "cjs"), the output code seems to be unchanged.

Output:

async function lazyCode() {
  const mod = await import('path');
}

Expected:

async function lazyCode() {
  const mod = await Promise.resolve().then(() => toModule(require('path')));
}

edit: looks like this happened on 0.10.0 when import and require behavior has been changed.

[hyrious]

Dynamic import() is available since node13.2. So if you need it to be transformed to require(), use --target=node12.

[lxsmnsyc]

Dynamic import() is available since node13.2. So if you need it to be transformed to require(), use --target=node12.

Even though it is supported in Node 13.2 and above, the code only runs for packages with "type": "module". The intended behavior when format: "cjs" is to always convert import statements to require, since CommonJS, regardless of the Node version, do not support import statements. Currently, this conversion only works for static imports and it used to be the case for the dynamic import expressions.

[clydin]

Dynamic import expressions are supported in both CJS and ESM (https://nodejs.org/docs/latest-v14.x/api/esm.html#esm_import_expressions).
This is particularly useful when ESM code needs to be used from within CJS code.

[lxsmnsyc]

In CommonJS modules, it can be used to load ES modules

Now that's the behavior I never wanted. I'll try readjusting the node target then

[evanw]

I'm going to close this because this is by design. Since import() and require() behave differently, it would be wrong to convert one into the other (unless of course you have to because it's unsupported and there's no other option). These are the differences I'm aware of:

• Doing import() on an ES module works but doing require() on an ES module doesn't work (described above).

• When resolving exports in package.json, import() uses the import condition while require() uses the require condition so using these two expressions with the same path can easily end up loading completely different files. You can learn more about this here: https://nodejs.org/api/packages.html#conditional-exports.

[lxsmnsyc]

Yes thank you @evanw, I went with node12 target so that it won't preserve the dynamic import.