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 <https://github.com/bevacqua/dragula>, 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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