How to run javascript in a webview from Swift

Question

I need my swift class to interact with the html and javascript in a wkwebview that it references, in particular, feed it a variable.

I thought I would start simply by trying to get the webview to fire an alert:

Here is the code:

let webView = WKWebView()

    override func viewDidLoad() {
      
        super.viewDidLoad()
         webView.uiDelegate = self
        webView.navigationDelegate = self as? WKNavigationDelegate
        if let url = Bundle.main.url(forResource: "tradingview", withExtension: "html") {
            webView.loadFileURL(url, allowingReadAccessTo: url.deletingLastPathComponent())
           
        }
       // Try one way in viewdidload. Compiles but doesn't do anything
         webView.evaluateJavaScript("alert('hello from the webview');");
    }
   
    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
//try another way. Also doesn't do anything
        webView.evaluateJavaScript("alert('hello from webview')"), completionHandler: nil)
    }
    override func loadView() {
        
        self.view = webView
    }

However, the webview is not firing an alert. What is wrong with the code or is there anything else you need to do to get Swift to run some javascript on a webview.

Thanks for any suggestions.

Omer Faruk Ozturk · Accepted Answer · 2020-07-18 21:14:35Z

2

You need to convert info in javascript alert into native UIAlert.

Add alert handler delegate described in WKUIDelegate.

func webView(_ webView: WKWebView,
             runJavaScriptAlertPanelWithMessage message: String,
             initiatedByFrame frame: WKFrameInfo,
             completionHandler: @escaping () -> Void) {

    let alert = UIAlertController(title: nil, message: message, preferredStyle: .alert)
    let title = NSLocalizedString("OK", comment: "OK Button")
    let ok = UIAlertAction(title: title, style: .default) { (action: UIAlertAction) -> Void in
        alert.dismiss(animated: true, completion: nil)
    }
    alert.addAction(ok)
    present(alert, animated: true)
    completionHandler()
}

And call like below (there is a type in your code);

func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
    webView.evaluateJavaScript("alert('hello from the webview')")
}

In Addition

There is a sample project that simulates two way communication between native and web in both way.

edited Jul 18, 2020 at 21:14

answered Jul 18, 2020 at 14:05

Omer Faruk Ozturk

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4 Comments

user6631314 Over a year ago

OK. You have answered the question so going to mark it correct. I didn't know about that delegate method. But my real goal is to pass a variable to webview from Swift and run a script on the webview. Can you suggest how to do that?

Omer Faruk Ozturk Over a year ago

The issue you asked is about showing an alert. So, first of all, if the answer is worked for you as you state, please don't forget to mark as accepted. This post may help you to build communication between webview and native.

user6631314 Over a year ago

Could not get example in link to work. Can you provide a simple example of calling evaluateJavaScript() from swift to run javascript in webview? I can ask separate question if you would like

Omer Faruk Ozturk Over a year ago

There is a sample project that simulates two way communication in both way.

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