Re: JsInterop and default settings in JS structures - how to handle?

Thanks Thomas,

I might have missed that reading the JsInterop specs ...

So, your basically saying that while in Java these two fields would be initialized to false and 0 by default, in JS they both end up undefined, when an object is created?

@JsType(isNative = true, name = "Object", namespace = JsPackage.GLOBAL)

class Options {      

    public int arg1; //defaults to 0 in Java, but 'undefined' in JS 

    public boolean arg2; //defaults to false in Java, but 'undefined' in JS

}

On Thursday, June 2, 2016 at 2:33:39 AM UTC-7, Thomas Broyer wrote:

On Thursday, June 2, 2016 at 1:15:57 AM UTC+2, Hristo Stoyanov wrote:

Hi all,

This is a pretty common in the JS world, but take a look at this JS library, which as part of its API has settings/options for configuration, where options are done with something with JS structure like:

{

  ...

  isContainer: function (el) { return false; }, 

  moves: function (el, source, handle, sibling) { return true; }, 

}

As you can see the callbacks have defaults that allows JS developers not to bother specifying them. Pretty neat! This is accomplished with code like:

function always () { return true; }
var o = options || {};
if (o.moves === void 0) { o.moves = always; }

Now, when I wrap such options object it in JsInterop:

@JsType(isNative = true, name = "Object", namespace = JsPackage.GLOBAL)

class Options {       

     

               ...

 

    @JsProperty

    public CallbackRet1<Boolean, Object> isContainer;

    @JsProperty

    public CallbackRet4<Boolean, Object, Object, Object, Object> moves;

              /** We need this trivial defaults to be singletons */

    public static final CallbackRet1<Boolean, Object> DEFAULT_IS_CONTAINER = o->false;

    public static final CallbackRet4<Boolean, Object, Object, Object, Object> DEFAULT_MOVES = (o1,o2,o3,o4)->true;

    /** A factory methods to set the defaults. Uh-oh!*/

              @JsOverlay

    final static public Options createDefault() {

       Options o = new Options();

       o.isContainer = DEFAULT_IS_CONTAINER;

       o.moves = DEFAULT_MOVES;

       return o; 

    }

 

}

Do I have to provide defaults for callbacks and other properties?  As you can see my current approach leads to verbose code and the getDeafult() method that I would really like to avoid.

What happens if I leave the properties uninitialized? What will the JS API see with such partially supplied options - undefined or null?  I tried putting @JsOptional on all of these properties, but this annotations in not meant for members.

What is the best strategy to handle such cases with JsInterop?

Also, why is JsInterop  not allowing me to initialize the fields at declaration?

With @JsType(isNative=true), fields simply map to JS properties, and the class constructor simply maps to the JS constructor, so there cannot be initialization code; see https://docs.google.com/document/d/10fmlEYIHcyead_4R1S5wKGs1t2I7Fnp_PaNaa7XTEk0/edit#heading=h.b1boa8c235km

This means that when you "new Options()" in Java, GWT will generate a "new $wnd.Object()" in JS. This in turns means that uninitialized "Java fields" will be left 'undefined' in JS.

(note: I haven't tried it, this is my interpretation reading the "JS interop spec", and what I would expect from GWT)

 

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