JavaScript/PHP file uploader

I'm writing a JavaScript/PHP file uploader and I want to start this project off on the right track. I've started with this, a JavaScript Uploader object which will handle Ajax calls, display progress, show error messages, etc. I'm just hoping to get some feedback on the way I'm setting up my scripts.

function Uploader(method) {

if(arguments.callee._singleton) return arguments.callee._singleton;
var _this = arguments.callee._singleton = this;

_this.opts = {
    form:"#uploader",
    filePath:"public/uploads/",
    errorCodes:{
        1:"No file/folder selected",
        2:"Invalid file/folder type",
        3:"File/folder exceeds upload size"
    }   
}

_this.methods = {

    init: function(options) {
        for(var o in options) {
            _this.opts[o] = options[o];
        }

        _this.methods.setup();
    },

    setup: function() {

    }

}   

if(_this.methods[method]) return _this.methods[method].apply(this, Array.prototype.slice.call(arguments, 1));
else if(typeof method === "object" || !method) return methods.init.apply(this, arguments);

}

Why not use an existing ajax file upload library, like Fine Uploader?

As for your code.
1)

I think you meant to return _this.methods.init.apply(this, arguments);.
2)

You should rewrite Uploader to not use arguments.callee for two reasons; it makes your code harder to read and for the browser to optimize.

StackExchange Code Review Q#8433, answer score: 2