iOS: evaluateJavaScript will not invoke function when parameter contains newline character

Question

The goal is to invoke a callback function inside a web page contained inside a WKWebView.

evaluateJavaScript breaks when its parameter contains the newline character, meaning the callback function never gets called.

Why is this?

userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) is invoked when the user presses a button on the web page.

func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
    let dict = message.body as! [String:AnyObject]
    let callback = dict["callback"] as! String

    // Fails
    let serializedClipboard = "hello\n" 

    // Works
    // let serializedClipboard = "hello" 

    webView!.evaluateJavaScript("\(callback)('\(serializedClipboard)')") { (object: Any?, error: Error?) -> Void in
        print("Done invoking \(callback)")
    }
}

Now that the question has been reformulated, it seems like a matter of escaping the newline inside of evaluateJavaScript ... one option is to encode to base64 (then decode on the JavaScript side), but is there a cleaner way to pass through newline characters? — Crashalot
– Crashalot, Commented Oct 27, 2016 at 19:37
why would you want to pass a new line in a callback parameter? — Vladimir M
– Vladimir M, Commented Oct 27, 2016 at 19:41
@VladimirM if you're serializing a paragraph of text, for instance. — Crashalot
– Crashalot, Commented Oct 27, 2016 at 19:43
Ah, you actually want to escape the \n. how to handle new-lines in JSON people seem to agree with your approach. — Vladimir M
– Vladimir M, Commented Oct 27, 2016 at 19:52

Crashalot · Accepted Answer · 2016-10-27 19:46:55Z

2

One option that seems to be working is to escape newline characters inside the parameter:

let escapedClipboard = serializedClipboard.stringByReplacingOccurrencesOfString("\n", withString: "\\n")

Please post suggestions if you see a cleaner solution.

answered Oct 27, 2016 at 19:46

Crashalot

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1 Comment

InkGolem Over a year ago

A big problem with this is that not all line break characters are \n.

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