CODEWITHSUNDEEP
rhino
bmargulies
bmargulies

Reputation: 100051

rhino dynamic properties for Javascript

In Rhino, I can add specific properties by defining js... functions on a Java class. What I'd like is to define a catchall function that gets called if a program goes to reference a property that hasn't been otherwise defined. Is there a way?

Upvotes: 0

Views: 1070

Answers (1)

jbeard4
jbeard4

Reputation: 12811

I don't think there is a way to express this concept using native syntax, even using Rhino/Spidermonkey proprietary extensions like getters and setters: https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide/Working_with_Objects#Defining_Getters_and_Setters

However, JavaScript is fairly easy to extend, and so I think you could get something pretty close by adding a method to Object.prototype to support this more advanced style method invocation. The following would seem to do what you want:

Object.prototype.invokeMethodOrDefault = function(methodName,argsArray){
    if(this[methodName] && typeof this[methodName] == "function"){
        //invoke method with given arguments
        this[methodName].apply(this,argsArray)
    }else{
        this.defaultMethod.apply(this,argsArray)
    }
}

//add a defaultMethod noop that can be overridden for individual subclasses
Object.prototype.defaultMethod = function(){print("In default method")} 

//test it
foo = {
    helloWorld:function(){
        print("hello world!")
        print("args:")
        for(var i=0,l=arguments.length;i<l;i++){
            print(arguments[i]);
        } 
    }
}
foo.invokeMethodOrDefault("thisMethodDoesNotExist",[]) 

foo.invokeMethodOrDefault("helloWorld",["arg1","arg2"]) 


bar = {
    helloWorld2:function(){
        print("hello world2!")
        print("args:")
        for(var i=0,l=arguments.length;i<l;i++){
            print(arguments[i]);
        } 
    },
    defaultMethod:function(){
        print("in new default method")
    }
}

bar.invokeMethodOrDefault("thisMethodDoesNotExist",[]) 

bar.invokeMethodOrDefault("helloWorld2",["arg1","arg2"])

Which prints the following:

In default method
hello world!
args:
arg1
arg2
in new default method
hello world2!
args:
arg1
arg2

Upvotes: 2

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