Recognize `.mjs` the same as `.js`

[surma]

.mjs is the file extension that is used for ES6 modules.

Emscripten should probably output an .mjs file when -s EXPORT_ES6=1 is set.

//edit: Emscripten currently outputs LLVM IR code when specifying -o file.mjs.

[sbc100]

Should be an easy fix..

[kripken]

Sounds reasonable to support it optionally. I'm less sure we should emit it with EXPORT_ES6 - are all othe tools doing that?

[surma]

To load an ES6 module in Node, an .mjs extension is required. Since that decision has been made, we are making an effort to make all tooling understand this and behave similarly.

I’d prefer to automatically output .mjs when EXPORT_ES6 is set, but at the very least Emscripten should not output LLVM IR when -o something.mjs is specified 😄

cc @mathiasbynens to keep me honest.

[mathiasbynens]

@surma nailed it:

I’d prefer to automatically output .mjs when EXPORT_ES6 is set, but at the very least Emscripten should not output LLVM IR when -o something.mjs is specified 😄

[kripken]

Thanks, makes sense. Ok, sgtm to emit .mjs in that case, and I see @sbc100 is already assigned here.

[dasa]

Should the output then work as a ES Module in Node?

I'm getting an error when I try that.

I compiled the sample shown at https://v8.dev/features/wasm-bigint using: emcc example.c --js-library example.js -o out.mjs -s WASM_BIGINT

I then started Node 14.15 using node --experimental-wasm-bigint and entered import("./out.mjs").then(m => { console.log(m.default()) }) and the output error is:

Promise { <pending> }
> (node:93802) UnhandledPromiseRejectionWarning: ReferenceError: __dirname is not defined
    at Module.<anonymous> (file:///Users/dasa/test/out.mjs:162:5)
    at REPL1:1:54

[wltsmrz]

Ran into that recently myself @dasa . I think the ES modules are meant to not contain Node-specific features like __dirname. The trick to get it to work apparently is:

import path from 'path'
const __dirname = path.dirname(new URL(import.meta.url).pathname)

[sbc100]

Looks like something we should fix. Would you mind opening a separate issue specifically about __dirname?

[curiousdannii]

Already raised: #11792