Pass JavaScript variable to Swift

Question

How would I go about changing the value of a Swift variable based on a JavaScript variable? (Passing a JavaScript variable to Swift)

My goal is simply to conduct an if statement using a JavaScript variable, and than edit the swift variable based on that.

Example in code of what I am trying to do:

var checkElement = false
webView.evaluateJavaScript("var element = document.getElementById(\"element\");"){ (value, error) in
        if let err = error {
            print(err)
        }
}
if (element != null){
checkElement = true
}

I understand this won't work due to element only existing in JavaScript. Although, how would I pass the element variable to Swift?

Stephen Rauch · Accepted Answer · 2018-11-26 03:31:11Z

I thought I would answer this myself.

First, ensure your class is conforming to the correct protocols: WKScriptMessageHandler is required and you may also need WKNavigationDelegate.

Before initializing your WKWebView add a userContentController to its configuration. This is what will act as a 'bridge' from your JavaScript to Swift.

var webView = WKWebView()
let configuration = WKWebViewConfiguration()
configuration.userContentController.add(self, name: "messageName")
webView = WKWebView(frame: .zero, configuration: configuration)

Now initialize the userContentController() function and handle the received content within it. Ex.

public func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
    print("Name: \(message.name)")
    print("Body: \(message.body as! String)")
}

Now within the JavaScript inside your evaluateJavaScript() add the following line to push whatever data to Swift:

window.webkit.messageHandlers['messageName'].postMessage('Message Body!');

Now, when that JavaScript line is called Swift will output the following:

Name: messageName
Body: Message Body!

shshsh · Accepted Answer · 2018-04-12 21:10:57Z

0

You can get variable in Swift code by interception clicked URL via UIWebViewDelegate method webView:shouldStartLoadWithRequest:navigationType:

Simulate click you can via iframe in JS.

Here is an example in Objective-C, but it will be same on Swift - http://iwearshorts.com/blog/how-to-call-uiwebview-from-javascript/

answered Apr 12, 2018 at 21:10

shshsh

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