A possible JsInterop issue in GWT 2.8 RC2

[Boris Brudnoy]

Hello all, 

I was tripped yesterday by a discrepancy in JsType field treatment between beta1 and rc2 releases, so I made a small Maven project reproducing it: https://github.com/bbrudnoy/jsinterop-test.

The problem is as follows: given a simple JsType-annotated class, HelloWorld:

@JsType(namespace = JsPackage.GLOBAL)

public class HelloWorld {

  public String hello = "Hello";

  public String world = "World";

}

passing an instance of it to a JavaScript function from GWT, as I do in App.java, the field names are preserved and usable in JavaScript, if I use beta1. Chrome Dev tools show this:

however, for the same code, if I change GWT version to 2.8.0-rc2, the fields become obfuscated and are no longer usable in JavaScript which worked previously:

 

Is this a JsInterop issue, or am I missing something in the way JsInterop has officially changed in RC2?

[Jens]

@JsType with isNative = false (the default) are probably treated as normal classes now if you do not use -generateJsInteropExports as compiler parameter. I guess it works again if you use the compiler parameter?

-- J.

[Boris Brudnoy]

Yes, field names return to being named in JavaScript as declared in Java after the addition of the -generateJsInteropExports compiler parameter. Why isn't this the default compiler behavior, though? After all, I followed the JsInterop spec, which, in @JsType section, states:

"The contract says that any instance behind this interface must have methods or properties with the original name in JavaScript (i.e not renamed, not pruned)."

"As the class is annotated with @JsType, it will preserve its original names for all of its public API. This makes the class easily accessible from JavaScript"

On Fri, Aug 19, 2016 at 3:38 PM Jens <jens.ne...@gmail.com> wrote:

@JsType with isNative = false (the default) are probably treated as normal classes now if you do not use -generateJsInteropExports as compiler parameter. I guess it works again if you use the compiler parameter?

-- J.

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BORIS BRUDNOY

Web Application Developer, Java/GWT Enthusiast (LinkedIn)

[Jens]

Because all these non native JsTypes are considered entry points to your application when they are exported and thus all code referenced by them can not be pruned and maybe some other optimization a can't be applied to it as well.

Now consider GWT libraries that use non native JsTypes to export their API to JavaScript so they can be used by an Angular UI or similar. If it would be the default then lots of apps would miss optimization opportunities just because they use the libraries and might not use any pure js at all.

This is especially harmful as the flag is an all or nothing flag. So you have to explicitly decide to export to JS. in the future you should also be able to define a regex which tells the compiler which classes to export. This will be helpful if you depend on multiple such libraries but your app only needs to export one if them as well.

-- J.

[Thomas Broyer]

FWIW, I believe this is https://github.com/gwtproject/gwt/commit/ca8ad7bc140bc23b237620c41d755ef787bd97b1 (i.e. on-purpose)

[Daniel Kurka]

Jens is spot on. We want people to explicitly use -generateJsInteropExports if they rely on exporting since it has a hit on code size.

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[Jens]

Jens is spot on. We want people to explicitly use -generateJsInteropExports if they rely on exporting since it has a hit on code size.

Maybe the mention of the parameter should be added to the JsType JavaDoc for a final 2.8 release.

-- J.

[Boris Brudnoy]

Thanks guys. A note on this should certainly make it into the public JsInterop doc, somewhere close to the definition of the JsType/JsMethod/JsProperty contract.

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[Goktug Gokdogan]

Document includes a comment about it in the examples and the section that describes the migration from 2.7 has an instruction to add the flag.

On Mon, Aug 22, 2016 at 7:17 AM, Boris Brudnoy <boris.brudnoy@healthometry.com> wrote:

Thanks guys. A note on this should certainly make it into the public JsInterop doc, somewhere close to the definition of the JsType/JsMethod/JsProperty contract.

On Mon, Aug 22, 2016 at 8:04 AM Jens <jens.ne...@gmail.com> wrote:

Jens is spot on. We want people to explicitly use -generateJsInteropExports if they rely on exporting since it has a hit on code size.

Maybe the mention of the parameter should be added to the JsType JavaDoc for a final 2.8 release.

-- J.

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BORIS BRUDNOY

Web Application Developer, Java/GWT Enthusiast (LinkedIn)

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[Daniel Gerson]

This tripped me up as well. I second adding a note to the Javadoc as Boris suggested.