How can I access a JS-exported module object from Java using GraalVM?

Question

I have some JS code that looks roughly like this:

let ssr = async (arg) => arg || "hello js";
export {ssr as default};

I want to access and call ssr from Java.

How can I do that?

I've been trying something like this:

var ctx = Context.newBuilder("js")
                .allowIO(true)
                .allowHostAccess(HostAccess.ALL)
                .build();

        var ssrResource = new String(Server.class.getResourceAsStream("/ssr.mjs").readAllBytes());

        ctx.eval(Source
                .newBuilder("js", ssrResource, "ssr.mjs")
                .build());
        var ssr = ctx.getBindings("js").getMember("ssr");

But this always returns null.

Very good question. I am also searching for an answer.

Martin
– Martin

2021-04-20 07:42:09 +00:00
Commented Apr 20, 2021 at 7:42 — Martin
– Martin, Commented Apr 20, 2021 at 7:42

Daniele Bonetta · Accepted Answer · 2020-05-06 19:53:50Z

3

Values exported from a module can be imported by another module using the import syntax. For example, you could have another file loading your module, like:

// -- some-module-file.mjs
import ssr from 'ssr.mjs'
ssr;

and then execute the file via:

File file = loadSomehow("some-module-file.mjs");
Source mainSource = Source.newBuilder("js", file).mimeType("application/javascript+module").build();
Value ssr = context.eval(mainSource);

Here, Value ssr is the value exported by your module with export {ssr as default};

answered May 6, 2020 at 19:53

Daniele Bonetta

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1 Comment

Renato Over a year ago

That seems helpful. I will try it and accept the answer if it works for me. Thanks.

BoriS · Accepted Answer · 2020-04-22 08:46:32Z

1

The following java code

import org.graalvm.polyglot.*;

class Main {
    public static void main(String[] args) {
        var ctx = Context.newBuilder("js").allowAllAccess(true).build();
        ctx.eval("js", "let ssr = async (arg) => arg || \"hello js\"");
        var v = ctx.getBindings("js").getMember("ssr");
        System.out.println(v.execute());
    }
}

outputs

Promise{[[PromiseStatus]]: "resolved", [[PromiseValue]]: "hello js"}

On GraalVM CE 20.0.0 so I assume there is something wrong with the way you build your Source object.

answered Apr 22, 2020 at 8:46

BoriS

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4 Comments

Renato Over a year ago

It doesn't work if you use the script as I posted, with an exports clause.

Renato Over a year ago

notice that this is a JS module I am trying to use (hence the file extension, mjs) I can't change the JS code.

Oleg Šelajev Over a year ago

maybe you could import the module and assign ssr from it to something global to pass it to the bindings?

BoriS Over a year ago

@Renato Ah, quite! Missed that, sorry.

user1336088 · Accepted Answer · 2023-09-07 12:19:28Z

1

Please look into testExportNamespace function at https://github.com/oracle/graaljs/blob/master/graal-js/src/com.oracle.truffle.js.test/src/com/oracle/truffle/js/test/interop/ESModuleTest.java

Hint is to use

allowExperimentalOptions(true) in Context builder
option(JSContextOptions.ESM_EVAL_RETURNS_EXPORTS_NAME, "true"); in Context builder
Set .mimeType(JavaScriptLanguage.MODULE_MIME_TYPE) in Source builder

Regards Saurabh

answered Sep 7, 2023 at 12:19

user1336088

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