Rhino, typeof and autoboxing confusion

Question

In a server side extension for SmartfoxServer (which uses Rhino) I had a piece of Javascript similar to this:

response["xpos"] = properties.get("xpos");
send(JSON.stringify(response));

This caused errors. What happened? Because properties is a Java Map, when a number is put into it, it's autoboxed into a java.lang.Double object. Therefore, when retrieving it and storing it in response["xpos"], the result is not a regular Javascript number but a JavaObject of type java.lang.Double. The JSON.stringify function was not meant to handle that and it crashed.

I fixed it with a hack like this:

response["xpos"] = 1.0 * properties.get("xpos");
send(JSON.stringify(response));

Is there a better way?

Answer 1

You can use Number(properties.get("xpos")), as in the following interactive console session:

js> x=java.lang.Double(2)
2.0
js> typeof x
object
js> x instanceof java.lang.Double
true
js> y=Number(x)
2
js> typeof y
number

This is how strings are typically converted in Rhino from java.lang.String to native JavaScript strings as well.