Evaluate and Resolve a Promise in WKWebView

This sums up every iOS development I've ever done. So I am very new to fast development or iOS development for that matter.

What I am trying to accomplish is behaving almost like jsonp when doing a cross domain ajax request in javascript (if you know how it works ...)

The problem I have is that I cannot evaluate the javascript and return something that behaves asynchronously. For example, get anything from indexedDB in webview

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after lvaring the view, typically from a nib.
    self.webview = WKWebView()
    self.i = 0

    let preferences = WKPreferences()
    let configuration = WKWebViewConfiguration()

    preferences.javaScriptEnabled = true

    configuration.preferences = preferences
    configuration.userContentController.add(self as WKScriptMessageHandler,name: "bridge")

    self.webview = WKWebView(frame: self.view.frame, configuration: configuration)
    webview.navigationDelegate = self
    webview.isHidden = true
    webview.load(URLRequest(url: URL(string: "http://example.com")!))

    /* 
    help...
    don't know how closure & completion Handler (callbacks) works in swift
    runjs("Promise.resolve({msg: 'hello world'})", completionHandler: (result) -> Void) {
        print(result) // expecting it to be {msg: 'hello world'}
    })
    */
}

      

        
        
        
      

    

My helper function

func runjs(input: String, completeHandler: Any) {
    self.i = self.i + 1
    // TODO: store the completeHandler in a some HashMap with `i` as the key

    let js = "Promise.resolve(" + input + ").then(res => webkit.messageHandlers.bridge.postMessage({i: " + String(self.i) + ", data: res}))"

    webview.evaluateJavaScript(js)
}

      

        
        
        
      

    

My message handler

/// Adds support for the WKScriptMessageHandler to ViewController.
extension ViewController: WKScriptMessageHandler {
    func userContentController(_ userContentController: WKUserContentController,
                               didReceive message: WKScriptMessage) {

        let json:NSDictionary = message.body as! NSDictionary
        let i:Int = json["i"] as! Int
        let data:NSDictionary = json["data"] as! NSDictionary

        // TODO: get the complete handler from a HashMap[i]
        // TODO: call the complete handler with data as argument
        // TODO: remove the complete handler from the HashMap
    }
}