Feature request: Add support for esm.

[coreyfarrell]

I'd like to request that esm be added if possible. Bad news I just tried adding it and couldn't get it to work. I added '.esm.mjs': 'esm', to extensions and '.esm.mjs' to jsVariantExtensions. This caused the following from gulp:

$ gulp
[21:05:15] Requiring external module esm
/home/coreyfarrell/test/gulpfile.esm.mjs:1
(function (exports, require, module, __filename, __dirname) { import log from 'gulplog';
                                                                     ^^^

SyntaxError: Unexpected identifier
    at new Script (vm.js:74:7)
    at createScript (vm.js:246:10)
    at Object.runInThisContext (vm.js:298:10)
    at Module._compile (internal/modules/cjs/loader.js:670:28)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:713:10)
    at Module.load (internal/modules/cjs/loader.js:612:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
    at Function.Module._load (internal/modules/cjs/loader.js:543:3)
    at Module.require (internal/modules/cjs/loader.js:650:17)
    at require (internal/modules/cjs/helpers.js:20:18)

The result was the same for gulp and npx gulp (global gulp-cli vs local gulp-cli).

[phated]

Thanks for opening the issue! I think the implementation will be closer to Babel (with the custom function wrapper) but haven't looked into it yet.

[phated]

@coreyfarrell I'm digging into this more but it seems like it'd require changes on the esm side because they expect the consumer to use a returned require-style function but we expect things to be registered onto a extension.

[phated]

Actually, I think I found the answer at standard-things/esm#433

[phated]

Need to do some testing on the changes using rechoir before I publish.

[coreyfarrell]

I just did some local testing against gulp, one issue I ran into it doesn't seem to respect any of the ways to set ESM options. To enable debug I had to edit interpret to use var esmLoader = hook(module, {debug: true});.

Note I'm looking into debug to find out why import {rollup} from 'rollup'; doesn't work. I think it's an esm bug, I'm able to reproduce this issue with a regular node -r esm script.mjs.

[phated]

@coreyfarrell I'm guessing they don't look up options when it's used programmatically - might want to check that too.

[coreyfarrell]

I got an explanation of the issue I was having with rollup. I had to drop my plan to use a dual mode main file in my own package, instead using "main": "index.js", "module": "index.mjs".

At this point I'm not sure how important it is to be able to set the ESM options, I'm able to use gulpfile.esm.js with the default options.

[coreyfarrell]

@phated Would you be willing to publish an updated version that includes .esm.js? I've been using this for a while and once I understood the limitations of the esm module it works great for me. Even if I'm pointing to a @next version I'd prefer to use an npm based dependency over gulpjs/interpret#master.

[phated]

Yeah, I can probably get something published this week.

[phated]

@coreyfarrell potentially great news, I'm just wrapping up a complete test suite for this project and should have the ESM update published as soon as my Window's CI succeeds.

[phated]

@coreyfarrell just published as 1.2.0!!