Quick, stand-alone deep extend implementation

extend.js

function extend () {
    var out = arguments[0],
        i, key, obj, val;

    for (i = 1; i < arguments.length; i += 1) {
        obj = arguments[i];

        for (key in obj) {
            if (obj.hasOwnProperty(key)) {
                val = obj[key];
                if (val && typeof val === 'object' && !val.length) {
                    out[key] = extend({}, val);
                } else {
                    out[key] = val;
                }
            }
        }
    }

    return out;
}