Flow: Need declaration for `System`.

[lixiaoyan]

Such as System.global, System.import...

[graue]

System.import support would really be handy. I don't think there's a proper way to work around this. The best I can come up with is

declare var System: {
  import: (module: string) => Promise<Object>;
}

and put up with no type-checking on the use of asynchronously imported modules. Preferably, Flow would know that if I System.import('./foo'), and ./foo.js looks like this:

export default function(a: number): number { return a+1; }
export const inc = 1;

then the return value of that import is

Promise<{
  default: (a: number) => number,
  inc: number,
}>

In other words, this is more than just a library definition. Flow needs to understand the semantics of System.import.

[andykenward]

Any update on this? Think I will just have to ignore System.import in flow for now.

[vkurchatkin]

@andykenward is there a spec for this?

[bloodyowl]

this isn't settled yet https://github.com/tc39/proposal-dynamic-import

[vkurchatkin]

@bloodyowl I know about this one, but I think that System is pretty much obsolete

[bloodyowl]

@vkurchatkin it seems so, yes

AFAIK no browsers supports it. if it's meant to be used with the SystemJS library, I'd advice to create the definitions in https://github.com/flowtype/flow-typed and wait for an official specification before adding anything in flow/lib

[andykenward]

I am using it for webpack 2 code splitting feature. I suppose I could switch to require.ensure.

Thanks for the quick response

[aackerman]

There is an open issue for dynamic import, https://github.com/facebook/flow/issues/2968

And global is at stage 3 of the spec proposal process, it would seem like this issue can be closed in favor of others.

[prewk]

I solved it with this declaration:

declare interface System {
    static import: (module: string) => Promise<{
        default: any,
        inc: number,
    }>
};

Might help someone! (Note: System.import() is deprecated in stable Webpack 2 and replaced by import(), I haven't started using this yet, however. Will that cause crazy module issues with Flow in the future?)

[vkurchatkin]

Will that cause crazy module issues with Flow in the future?)

Most definitely. You code won't even parse until this feature is implemented in Flow. See https://github.com/facebook/flow/issues/2968

[vkurchatkin]

Closing since System proposal is abandoned