Dependency Injection in JavaScript

di.js

var di = (function Dein() {
    var FN_ARGS = /^function\s*[^\(]*\(\s*([^\)]*)\)/m;
    var FN_ARG_SPLIT = /,/;
    var FN_ARG = /^\s*(_?)(\S+?)\1\s*$/;
    var STRIP_COMMENTS = /((\/\/.*$)|(\/\*[\s\S]*?\*\/))/mg;

    var _register = {};

    function anno(fn, strictDi, name) {
        var fnText, argDecl, args;
        if (fn.length) {
            fnText = fn.toString().replace(STRIP_COMMENTS, '');
            argDecl = fnText.match(FN_ARGS);
            args = argDecl[1].split(FN_ARG_SPLIT);
            return args.map(function(arg) {
                return arg.trim();
            });
        }
        return [];
    }

    function fnName(fn) {
        return fn.name;
    }

    function register(fn) {
        var name = fnName(fn);
        _register[name] = fn;
    }

    function resolve(fn) {
        var args = anno(fn);
        var a = args.map(function(name) {
            var f = _register[name];
            return resolve(f);
        });
        return fn.apply(null, a);
    }
    resolve.register = register;

    return resolve;
}());

di.register(function dbconfig() {
    return {
        host: 'localhost',
        port: 1337
    };
});

di.register(function db(dbconfig) {
    return function(user, pw) {
        console.log(dbconfig, user, pw);
        return true;
    };
});

di.register(function log() {
    return function(str) {
        console.log(str);
    };
});

function app(log, db) {
    return function() {
        if(db('user', 'pw')) {
            log('connected!');
        } else {
            log('could not connect');
        }
    };
}
var a = di(app);
a();