JS рекурсивное расширение

extendDeep.js

function extendDeep(parent, child) {
    var
        toStr = Object.prototype.toString
        , astr = '[object Array]'
        , i
    ;
    
    child = child || {};
    
    for(i in parent) {
        if(parent.hasOwnProperty(i)) {
            if(typeof parent[i] === "object") {
                child[i] = (toStr.call(parent[i]) === astr) ? [] : {};
                extendDeep(parent[i], child[i]);
            } else {
                child[i] = parent[i];
            }
        }
    }
    
    return child;
}