Explore supporting ES import() proposal

[mohsen1]

Dynamic import proposal is in early stages but it will require TypeScript to support it in order to be usable in TypeScript based apps.

Basic syntax:

import('./my-module.ts').then(({export1, export2}) => {
  
});

[mhegazy]

This is a proposal that we are following in the committee. I would expect us to start looking into this early next year.

also referenced in #11611. i think we just need one issue to track this.

[Jessidhia]

Stubbing it such that it is not a syntax error, has apparent type (request: string) => Promise<any>, and is emitted as-is could be useful for using it with e.g. https://github.com/airbnb/babel-plugin-dynamic-import-webpack or eventually with webpack/webpack#3098 in webpack 2; but I don't know how good or bad an idea that is.

[aluanhaddad]

@Kovensky anyone can easily write that stub should they need it so I don't think its declaration belongs in the language any more than require, define, or System.import.

[Jessidhia]

@aluanhaddad not quite. Just writing a ( after import causes a syntax error, regardless of anything you try to do declaration-wise. This needs compiler support, and definitely behind an experimental flag if it's ever done as a stub.

[aluanhaddad]

@Kovensky I don't think I have actually tried to write it like that, thanks for explaining that this isn't possible.

[Jessidhia]

Dynamic import() support landed in webpack master and should be in the next webpack 2 beta. It was also promoted to stage-3 as of the last latest TC39 meeting.

[saschanaz]

It was also promoted to stage-3 as of the last TC39 meeting

That means SystemJS may update their API to match it! :D

[chicoxyzzy]

SystemJS can't update their API to match proposal because import() is a SyntaxError. TypeScript's parser should definitely support this syntax so people will be able to transpile dynamic imports to SystemJS / CommonJS / Webpack 1 require.ensure() / use WebPack 2 code splitting

[chicoxyzzy]

has apparent type (request: string) => Promise<any>

it's (specifier: any) => Promise<any>, according to latest spec, it's totally valid to pass anything to it, ToString will be applied to specifier

[chicoxyzzy]

Can we have a compiler option to support this syntax?

[chicoxyzzy]

Sadly we'll loose type information when specifier should be computed :(

[Jessidhia]

There are talks about attaching meta-properties to import, similarly to what was done with new for new.target. It might be better represented (for forward compatibility) as an interface with that call signature, but this might be thinking too far ahead.

See estree/estree#137 (comment)