loading.swift

struct ArticleListViewModel {
    
    var title :String? = "Articles"
    var articles :[ArticleViewModel] = [ArticleViewModel]()
}

extension ArticleListViewModel {
    
    init(articles :[ArticleViewModel]) {
        self.articles = articles
    }
    
    func loadArticles(callback :(([Article]) -> ())) {
        
        URLSession.shared.dataTask(with: url) { data, response, error in
            
            if let data = data {
                
                let json = try! JSONSerialization.jsonObject(with: data, options: [])
                let dictionary = json as! JSONDictionary
                
                let articleDictionaries = dictionary["articles"] as! [JSONDictionary]
                
                articles = articleDictionaries.flatMap { dictionary in
                    return Article(dictionary :dictionary)
                }
            }
            
            DispatchQueue.main.async {
                callback(articles)
            }
    }
}