GWT to Javascript conversion

In javascript console if I do this,

   a = [1,2,3]
   Object.prototype.toString.call(a) // gives me "[object Array]"
   typeof a  // gives me "object"

If I create an arraylist in GWT and pass it to a native method and do this,

// JAVA code
   a = new ArrayList<Integer>();
   a.push(1);
   a.push(2);

   //JSNI code
    Object.prototype.toString.call(a) // gives me "[object GWTJavaObject]"
    typeof a // returns "function"

What exactly is the difference between the both? Is GWTJavaObject exactly similar to Array ?

Why do typeof return " object " in pure javascript but " function " in GWT?

Summary question is, what exactly are the GWT objects converted to in Javascript? Full code is here.

      public void onModuleLoad()
        {
                List<Integer> list = new ArrayList<Integer>();
            list.add( new Integer( 100 ) );
            list.add( new Integer( 200 ) );
            list.add( new Integer( 300 ) );

            Window.alert(nativeMethodCode( list ));
                Window.alert(nativeMethodCode2( list ));
        }

        public static final native Object nativeMethodCode( Object item )
        /*-{
            return Object.prototype.toString.call(item);
        }-*/;

        public static final native Object nativeMethodCode2( Object item )
        /*-{
            return typeof item;
        }-*/;

---

An ArrayList in GWT is not translated to a pure JS array: it's a class extending AbstractList and implementing a bunch of interfaces, and this information should be kept when translated to JS so that instanceof checks (in your Java code; eg instanceof List or instanceof RandomAccess ) still work as expected. An ArrayList is thus implemented as a wrapper around a JS array, see https://code.google.com/p/google-web-toolkit/source/browse/tags/2.5.0/user/super/com/google/gwt/emul/java/util/ArrayList.java.

Note that a Java array is translated to a JS array, but be very careful about what you do to it in JSNI as you could break further Java assumptions (eg that an array has a fixed size).

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