Completion handler paradigm in Swift 4.0.

This tutorial we are study about how to define the completion handler function and how it use. Here we are define a function in which call a webservice and handle it's response.

Completion Handler :

func getList(_ completion: @escaping (NSArray) -> ()) {

        let urlPath = "url"
        guard let url = URL(string: urlPath) else { return }

        let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
            guard let data = data else { return }
            do {
                if let jsonResult = try JSONSerialization.jsonObject(with: data, options: JSONSerialization.ReadingOptions.mutableContainers) as? NSDictionary {
                    let results = jsonResult["genres"] as! NSArray
                    print(results)
                    completion(results)
                }
            } catch {
                //Catch Error here...
            }
        }
        task.resume()
    }

Handle Response : 

getList { (array) in
     // Lists of results.
     print(array)
}

Any query about it send me message.

Thanks.