Enhancement Proposal: dynamic imports

[kaicataldo]

Now that dynamic imports are now stage 3 and are used by Webpack v2 for code splitting, I'd like to propose we add support for this in Espree/ESLint behind an option like experimentalDynamicImport: true.

An Acorn plugin already exists, and it looks like it's well used: https://www.npmjs.com/package/acorn-dynamic-import

[kaicataldo]

For reference, at my place of work, we're using babel-eslint just for dynamic imports right now.

[mysticatea]

My state is negative about supporting stage 3. There are some reasons.

• there is a precedent that a stage 3 proposal dropped; simd
• after we implemented rest spread properties, AST of the syntax changed without compatibility. Now, there are 3 kinds of AST; espree's, babel-eslint's, and ESTree's. It's confusing.
• stage 3 is unstable. Chrome beta enables rest properties by default, but the syntax has been changed in the last tc39 meeting. Chrome's syntax is now non-standard.
• babel-eslint is supporting experimental syntax.

[kaicataldo]

@mysticatea In general, I agree. This feels like a special case to me because of Webpack. Personally, I think it doesn't feel great to have to use another parser to get code splitting in such a ubiquitous tool.

[mysticatea]

Doesn't webpack support require?

[kaicataldo]

Yeah, it's also possible to use require.ensure() instead of import(). I suppose that's a fair argument.

[soda0289]

Would it be possible to make espree an acorn plugin? Then you could just use acorn with eslint and use any plugin you wanted.

[kaicataldo]

@soda0289 Relevant discussion: #334

[nzakas]

Also 👎 Our position has always been that using experimental features requires using Babel. Babel does a really good job at supporting them, and as long as Babel-ESLint exists, I don't think we should change our policy on this.

[kaicataldo]

With 2 👎s from TSC members, in going to close this.

[tschaub]

Should a new issue be opened now that dynamic imports are at Stage 4 (tc39/proposal-dynamic-import#78)?

[mdjermanovic]

@tschaub espree supports dynamic imports since v6.1.0, if the ecmaVersion is set to 2020 or higher.

Ref #415

[tschaub]

Thanks, @mdjermanovic.

Different subject, but I’m curious if there is discussion somewhere about why the default for ecmaVersion is kept so low.

[kaicataldo]

@tschaub It's been discussed many times in the eslint/eslint repo (and we've had proponents both for keeping ecmaVersion as it is currently and setting to latest), but the summary is that we've erred on the safer side of things by making new syntax opt-in rather than opt-out. This means that someone running their code in an environment that doesn't support the latest syntax would never accidentally push code that couldn't execute to production.