Get Javascript function response in iOS using Swift

If you are using WKWebView you can call javascript by using

webView.evaluateJavaScript("YourJavaScript",completionHandler : nil )

For UIWebView you can use

  webview.stringByEvaluatingJavascriptFromString : @"YourJavaScript";

These two links (first, second) are helped to me solve my problem.

html/javascript code:

function bar(qq){
    document.getElementById('foo').innerHTML = qq;
}

<div id="foo"></div>

My ViewController looks like this:

class ViewController: UIViewController, WKNavigationDelegate, WKUIDelegate {

    var webView: WKWebView

    required init(coder aDecoder: NSCoder) {
        self.webView = WKWebView(frame: CGRect.zero)
        super.init(coder: aDecoder)!
    }

    override func loadView() {
        super.loadView()

        let userContentController = WKUserContentController()

        let source = "bar('Hello from swift');"
        let userScript = WKUserScript(source: source, injectionTime: WKUserScriptInjectionTime.atDocumentEnd, forMainFrameOnly: true)
        userContentController.addUserScript(userScript)

        let configuration = WKWebViewConfiguration()
        configuration.userContentController = userContentController
        self.webView = WKWebView(frame: self.view.frame, configuration: configuration)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        view.addSubview(webView)

        webView.translatesAutoresizingMaskIntoConstraints = false
        let height = NSLayoutConstraint(item: webView, attribute: .height, relatedBy: .equal, toItem: view, attribute: .height, multiplier: 1, constant: 0)
        let width = NSLayoutConstraint(item: webView, attribute: .width, relatedBy: .equal, toItem: view, attribute: .width, multiplier: 1, constant: 0)
        view.addConstraints([height, width])

        let path = Bundle.main.path(forResource: "foldername/index", ofType: "html")!
        let url = URL(fileURLWithPath: path)

        webView.load(URLRequest(url: url))
        webView.allowsBackForwardNavigationGestures = true
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

var AppiwebScript = function() {//in some_file.js
   //TO DO
};

//below is code for xcode
let jScript = "AppiwebScript();"//name js function, in js file
let str_val =  mainWebView.stringByEvaluatingJavaScript(from: jScript)//handeleng js function