--format=cjs behave differently depends on node version

[zen0wu]

Not sure if I configured incorrectly, but when we set target to different node version, the transform behavior on await import is different. I didn't find a way to configure target to node14 that keep the await import behavior to commonjs.

Sample code

import optimist from 'optimist';

async function f() {
  return await import('optimist');
}

f().then(o => {
  console.log('await import', optimist.parse);
  console.log('await import', o.parse);
})

Transform output

--target=node12

async function f() {
  return await Promise.resolve().then(() => __toModule(require("optimist")));
}

--target=node14

async function f() {
  return await import("optimist");
}

tsc output (module=commonjs, despite of node version)

async function f() {
  return await Promise.resolve().then(() => __importStar(require("optimist")));
}

Run output

❯ node_modules/.bin/esbuild --format=cjs --platform=node --target=node14 test.ts | volta run --node 14 node -
await import [Function: bound ]
await import undefined

❯ node_modules/.bin/esbuild --format=cjs --platform=node --target=node12 test.ts | volta run --node 12.21.0 node -
await import [Function: bound ]
await import [Function: bound ]

[hyrious]

Dynamic import is available in node13, so it is kept when the target node version is higher than that.
tsc actually does not have an option to specify target node version, it only has es versions like ES6 and ES2020.

To speak the difference of import() and require(), when the imported library is pure ESM (like the ones from Sindre Sorhus'), require() won't work. However import() works both for CJS and ESM inputs.

[zen0wu]

thanks for the context. I think it's just surprising to me that esbuild's output varies based on node version. Other tools like TSC exposes option like "module":"commonjs", and emits code that works with the option in any case.

I haven't looked into every piece of our internal code to see whether it's possible to migrate them to respect await import, but in the case it might be hard, we're stuck with target=node12 even if we want to upgrade to node 14.

[clydin]

Native dynamic import expressions are critical to CommonJS/ESM interoperability. TypeScript’s (tsc) current behavior unfortunately breaks this interoperability.
To support ESM code use from CommonJS, Node.js considers dynamic import expressions as a supported part of the CommonJS module system (https://nodejs.org/api/esm.html#esm_import_expressions).

[evanw]

See #1084 for additional context.

[zen0wu]

Thanks, I guess this is a won't fix, closing.