Method missing in JS

Question

In python I can do something like this:

class Converter(object):
    def __init__(self, amount):
        self.amount = amount

    def rupy(self):
        return self.amount * 2

    def __getattr__(self, *args, **kwargs):
        if args[0] == 'rupies':
            return self.rupy

Is JS provide some way to achieve the same behavior? I googled a bit and found article about noSuchMethod but it works only in Firefox.

Edit: I don't wan't to have aliases I want to have a way to handle method missing generically

check: http://stackoverflow.com/questions/387707/whats-the-best-way-to-define-a-class-in-javascript — bitoiu, Apr 02 '14 at 08:48
My question is concrete and I can't find an answer in topic provided by you — kharandziuk, Apr 02 '14 at 08:51

Paul S. · Accepted Answer · 2014-04-02T09:14:30.483

Short answer

Does JavaScript have an equivalent to __getattr__?

No :(

Long answer

It looks like you just want to map aliases, JavaScript has no problem with adding properties to things like this

// set up
function Converter(amount) {
    this.amount = amount;
}
Converter.prototype.rupy = function () {
    return this.amount * 2;
};
// add aliases
var original = 'rupy', aliases = ['rupies'], i;
for (i = 0; i < aliases.length; ++i)
    Converter.prototype[aliases[i]] = Converter.prototype[original];

Now

var foo = new Converter(1);
foo.rupies(); // 2

and have

foo.rupies === foo.rupy; // true

Future answer

In ECMAScript 6 (Harmony) we have Proxies

Constructor.prototype = Proxy(Constructor.prototype, {
    'get': function (target, name, child) {
            var o = child || target; /* =proxy? if proxy not inherited? */
            if (name in target) return o[name];
            if (name === 'rupies') return o['rupy'];
            return;
        },
    'set': function (target, name, val, child) {
            return target[name] = val;
        },
    'has': function (target, name) {
            return name in target; // do you want to make 'rupies' visible?
        },
    'enumerate': function (target) {
            for (var key in target) yield key;
        }
});

Method missing in JS

1 Answers1