I'm looking to be able to extend the function prototype in javascript (that is to say, add a function to all functions). The purpose is to convert it into a format for exchange between another language (namely ruby, which can only municate through strings [in this particular setting]). I've already got a system so I can pass around other types by defining a to_js method on ruby objects and a to_ruby method on javascript objects, like so

Number.prototype.to_ruby = function () { return this.toString(); }

This is working for everything else I want it to, but not for functions. I can get it to work in chrome by doing the following:

_empty = function() {};
_empty.__proto__.to_ruby = function () {
    return 'JSFunction.new(' + this.toString().to_ruby() + ')';
};

But this does not work in IE (which is a requirement of the system).

I know I have an object somewhere keeping a track of functions by an ID or similar, but I can't guarantee that they will be used with the same instance that created them.

All else failing I could just write a function to special case deal with it (ie, isFunction(instance) ? fn_to_ruby(instance) : instance.to_ruby(), but I'd rather keep this model if possible.

I'm looking to be able to extend the function prototype in javascript (that is to say, add a function to all functions). The purpose is to convert it into a format for exchange between another language (namely ruby, which can only municate through strings [in this particular setting]). I've already got a system so I can pass around other types by defining a to_js method on ruby objects and a to_ruby method on javascript objects, like so

Number.prototype.to_ruby = function () { return this.toString(); }

This is working for everything else I want it to, but not for functions. I can get it to work in chrome by doing the following:

_empty = function() {};
_empty.__proto__.to_ruby = function () {
    return 'JSFunction.new(' + this.toString().to_ruby() + ')';
};

But this does not work in IE (which is a requirement of the system).

I know I have an object somewhere keeping a track of functions by an ID or similar, but I can't guarantee that they will be used with the same instance that created them.

All else failing I could just write a function to special case deal with it (ie, isFunction(instance) ? fn_to_ruby(instance) : instance.to_ruby(), but I'd rather keep this model if possible.

• javascript
• prototype

• Hah! I just happen to be looking into the same thing. SketchUp Ruby <-> JavaScript bridge. :D – thomthom Commented Jun 5, 2013 at 12:16

3 Answers 3

As Slace said, you can add the method to all Objects by adding it to Object.prototype, but that isn't really kosher as it may affect badly written for..in loops.

You can add it just to functions via Function.prototype:

Function.prototype.to_ruby = function() {
  return this.toString();
}

However there is a general rule that you shouldn't modify built-in objects, mostly because you never know when it will e back to haunt you (e.g. a new version of ECMAScript implements a property with the same name). Perhaps you are better off to write a single toRuby function:

function toRuby(obj) {
  return obj.toString();
}

but you can also also use the + operator to concatenate with a string to call the toString method implicitly:

'' + obj; // returns obj.toString()

which will return exactly the same result as both the above. Your choice.

__proto__ is not a standard property. Try this approach:

(function(){}).constructor.prototype.to_ruby = function(){
    return 'JSFunction.new(' + this.toString().to_ruby() + ')';
};

The __proto__ is not part of any JavaScript standard it's just a pesudo-standard that some of the browser manufacturers have decided to implement. IE is one that hasn't implemented it.

If you want to modify any type in the JavaScript type system then you'll have to modify the Object prototype:

Object.prototype.foo = function () { console.log('foo'); };
(1).foo();
'asd'.foo();
(true).foo();
({ bar: 'baz' }).foo();