JsInterop Object Literal

[Brandon Donnelson]

Can JsInterop create an object literal? 

var foo = {a:0, b:1};

[Brandon Donnelson]

I found a doc talking about object literal creation https://docs.google.com/document/d/1DFrC-GtcK7cu6DGxaWCswvb2fai9cnrWPvGcdgsKlBw/edit. 

[Ray Cromwell]

Right now, the best you can do is

@JsType(isNative = true, namespace =JsPackage.GLOBAL, name = "Object")
class MyLiteral {
}

And put js properties on the object

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[Brandon Donnelson]

Thank you! That's awesome. 

On Sunday, March 20, 2016 at 12:08:10 AM UTC-7, Ray Cromwell wrote:

Right now, the best you can do is

@JsType(isNative = true, namespace =JsPackage.GLOBAL, name = "Object")
class MyLiteral {
}

And put js properties on the object


On Sat, Mar 19, 2016 at 11:11 PM, Brandon Donnelson
<branfl...@gmail.com> wrote:
> I found a doc talking about object literal creation
> https://docs.google.com/document/d/1DFrC-GtcK7cu6DGxaWCswvb2fai9cnrWPvGcdgsKlBw/edit.
>
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> You received this message because you are subscribed to the Google Groups
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[Paul Stockley]

I think having a really succinct way of dealing with JS Object literals will be key to inter-op with existing java script code. Is the plan to land the enhanced support in the 2.x code base or will this be j2cl only? I really hope it will be included on 2.x

In the meantime I have come up with a few alternatives that can be implemented now. I will post details later this week.

[Paul Stockley]

I have come up with 3 approaches to creating object literals given the current JsInterop capabilities:

1) Construct and set the fields individually

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

   int field1;

   String field2;

}

SomeObjectLiteral o = new SomeObjectLiteral();

o.field1 = 1;

o.field2 = "Some value";

2) Define a fluent interface

@JsType(isNative = true, namespace = JsPackage.GLOBAL, name = "Object")
class SomeObjectLiteral {
   int field1;
   String field2;


   @JsOverlay
   public final SomeObjectLiteral Field1(int v) {
      field1 = v;
      return this;
   }

   @JsOverlay
   public final SomeObjectLiteral Field2(String v) {
      field2 = v;
      return this;
   }
}

You can then write

new SomeObjectLiteral().Field1(1).Field2("A value");

Note I didn't call the setter setFieldx. This is because you currently get a runtime error if you do this.


2) Use an ObjectLiteral Helper

You can define a helper similar to

public class ObjectLiteral {
    public static <O> O $(O base, Object ...fieldValues) {
        String fieldName = null;

        for(Object f : fieldValues) {
            if (fieldName == null)
                fieldName = (String)f;
            else {
                if (f instanceof Integer)
                    setField(base, fieldName, ((Integer) f).intValue());
                else if (f instanceof Double)
                    setField(base, fieldName, ((Double) f).doubleValue());
                else if (f instanceof Boolean)
                    setField(base, fieldName, ((Boolean) f).booleanValue());
                else
                    setField(base, fieldName, f);

                fieldName = null;
            }
        }

        return base;
    }

    private final static native void setField(Object literal, String fieldName, int i) /*-{
        literal[fieldName] = i;
    }-*/;

    private final static native void setField(Object literal, String fieldName, double d) /*-{
        literal[fieldName] = d;
    }-*/;

    private final static native void setField(Object literal, String fieldName, boolean b) /*-{
        literal[fieldName] = b;
    }-*/;

    private final static native void setField(Object literal, String fieldName, Object o) /*-{
        literal[fieldName] = o;
    }-*/;
}

You can then write

import static com.xxx.ObjectLiteral.$;

@JsType(isNative = true, namespace = JsPackage.GLOBAL, name = "Object")
class SomeObjectLiteral {
   int field1;
   String field2;
}

$(new SomeObjectLiteral(), "field1",123, "field2","some value")

You would probably want to add some more error checking to the helper. This approach probably isn't 
particularly efficient, especially if you pass a lot of field values that get boxed into Object primitives. 
It would be nice if the compiler unboxed varargs passed to isNative=true methods. If this was true you
could write a much more efficient javascript version.

[Ignacio Baca Moreno-Torres]

If your concert is to be able to write one-line initializers, and you are using java8 syntax you also do something like that:

public static <T> T apply(T t, Consumer<T> fn) {
    fn.accept(t);
    return t;

}

@JsType(isNative = true, namespace = JsPackage.GLOBAL, name = "Object")
class SomeObjectLiteral {
    int field1;
    String field2;
}

{

    SomeObjectLiteral sol = apply(new SomeObjectLiteral(), o -> { o.field1 = 1; o.field2 = "str"; });

}

Copied from kotlin (although without method extensions and method inline is not the same ;)), this is usable for client and server code when you need to initialize small pojos without fluent api.

[Paul Stockley]

That's a nice approach.

[Brandon Donnelson]

Thanks Paul. I haven't seen use of the JsOverlay yet, that's nifty. 

Nice Ignacio. 

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[Jens]

If your concert is to be able to write one-line initializers, and you are using java8 syntax you also do something like that:

public static <T> T apply(T t, Consumer<T> fn) {
    fn.accept(t);
    return t;
}

@JsType(isNative = true, namespace = JsPackage.GLOBAL, name = "Object")
class SomeObjectLiteral {
    int field1;
    String field2;
}

{
    SomeObjectLiteral sol = apply(new SomeObjectLiteral(), o -> { o.field1 = 1; o.field2 = "str"; });

}

Copied from kotlin (although without method extensions and method inline is not the same ;)), this is usable for client and server code when you need to initialize small pojos without fluent api.

Looks like a good example how to over-use lambdas. IMHO its just more complicated without any added value if its just for initialization.

SomeObjectLiteral sol = apply(new SomeObjectLiteral(), o -> { o.field1 = 1; o.field2 = "str"; });

SomeObjectLiteral sol = new SomeObjectLiteral(); sol.field1 = 1; sol.field2 = "str";

Old school is even shorter ;-) 

-- J.

[Ray Cromwell]

Use an annotation processor

@AutoLiteral

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

class MyFoo {
public int field1, field2;

}

@Generated(...)
@JsType(IsNative = true, namespace = JsPackage.GLOBAL, name = "Object")
class MyFooLiteral extends MyFoo {
public MyFooLiteral make() { return new MyFooLiteral(); }
@JsOverlay
final public MyFooLiteral field1(int x) { field1 = x; }
@JsOverlay
final public MyFooLiteral field2(int x) { field2 = x; }
}


callFunc(MyFooLiteral.make().field1(42).field2(99));

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