Docs/examples for JSAdapter

[Jim Laskey (Oracle)]

In general the Nashorn docs start here. https://wiki.openjdk.java.net/display/Nashorn/Nashorn+Documentation, but as you point out, we seem to be lacking JSAdapter details.  I should start an FAQ.

From the javadoc (cd make; ant javadoc # ./dist/javadoc/index.html)

public final class NativeJSAdapter
extends ScriptObject
This class is the implementation of the Nashorn-specific global object named JSAdapter. It can be thought of as the Proxy equivalent for JavaScript. NativeJSAdapter calls specially named JavaScript methods on an adaptee object when property access/update/call/new/delete is attempted on it. Example:
    var y = {
                __get__    : function (name) { ... }
                __has__    : function (name) { ... }
                __put__    : function (name, value) {...}
                __call__   : function (name, arg1, arg2) {...}
                __new__    : function (arg1, arg2) {...}
                __delete__ : function (name) { ... }
                __getIds__ : function () { ... }
            };

    var x = new JSAdapter(y);

    x.i;                        // calls y.__get__
    x.foo();                    // calls y.__call__
    new x();                    // calls y.__new__
    i in x;                     // calls y.__has__
    x.p = 10;                   // calls y.__put__
    delete x.p;                 // calls y.__delete__
    for (i in x) { print(i); }  // calls y.__getIds__
 
JavaScript caller of adapter object is isolated from the fact that the property access/mutation/deletion are really calls to JavaScript methods on adaptee.

JSAdapter constructor can optionally receive an "overrides" object. Properties of overrides object is copied to JSAdapter instance. When user accessed property is one of these, then adaptee's methods like __get__, __put__ etc. are not called for those. This can be used to make certain "preferred" properties that can be accessed in the usual/faster way avoiding proxy mechanism. Example:

     var x = new JSAdapter({ foo: 444, bar: 6546 }) {
          __get__: function(name) { return name; }
      };

     x.foo;           // 444 directly retrieved without __get__ call
     x.bar = 'hello'; // "bar" directly set without __put__ call
     x.prop           // calls __get__("prop") as 'prop' is not overridden
 
It is possible to pass a specific prototype for JSAdapter instance by passing three arguments to JSAdapter constructor. So exact signature of JSAdapter constructor is as follows:
     JSAdapter([proto], [overrides], adaptee);
 
Both proto and overrides are optional - but adaptee is not. When proto is not passed JSAdapter.prototype is used.
As well as the test ./test/script/basic/jsadapter.js

var obj = new JSAdapter() {
    __get__: function(name) {
        print("getter called for '" + name + "'"); return name;
    },

    __put__: function(name, value) {
        print("setter called for '" + name + "' with " + value);
    },

    __call__: function(name, arg1, arg2) {
        print("method '" + name + "' called with " + arg1 + ", " + arg2);
    },

    __new__: function(arg1, arg2) {
        print("new with " + arg1 + ", " + arg2);
    },

    __getIds__: function() {
        print("__getIds__ called");
        return [ "foo", "bar" ];
    },

    __getValues__: function() {
        print("__getValues__ called");
        return [ "fooval", "barval" ];
    },

    __has__: function(name) {
        print("__has__ called with '" + name + "'");
        return name == "js";
    },

    __delete__: function(name) {
        print("__delete__ called with '" + name + "'");
        return true;
    }
};

// calls __get__
print(obj.foo);

// calls __put__
obj.foo = 33;

// calls __call__
obj.func("hello", "world");

// calls __new__
new obj("hey!", "it works!");

for (i in obj) {
    print(i);
}

for each (i in obj) {
    print(i);
}

var x = "foo" in obj;
print(x);

var y = "js" in obj;
print(y);

print(delete obj.prop);

print(obj["js"]);
obj["js"] = "javascript";
print(obj["javascript"]);

Hope that helps.  Is there a specific question?

Cheers,

-- Jim

On 2013-10-22, at 11:50 AM, Rick Bullotta <rick.bullotta at thingworx.com> wrote:

> Hi, all.
> 
> I've been searching everywhere for any form of documentation or substantive examples as to how JSAdapter works in Nashorn, as it is an essential piece of the puzzle for many of us who will naturally be migrating from Rhino.
> 
> Can anyone provide and additional info?
> 
> Thanks,
> 
> Rick
> ThingWorx
>