In an Xcode 26.4 + iOS 26.x environment, I called evaluateJavaScript inside webView(_ webView: WKWebView, didCommit navigation: WKNavigation!) and got the following error:
Printing description of error:
▿ Optional<Error>
- some : Error Domain=WKErrorDomain Code=4 "A JavaScript exception occurred" UserInfo={WKJavaScriptExceptionLineNumber=0, WKJavaScriptExceptionMessage=TypeError: undefined is not a function, WKJavaScriptExceptionColumnNumber=0, NSLocalizedDescription=A JavaScript exception occurred})
However, this worked fine in earlier versions before Xcode 26.4 (> 26.0 and < 26.4, though I do not remember the exact version), still with iOS 26.x.
It also works fine in an Xcode 26.4 + iOS 18.x environment.
And if I add a slight delay using DispatchQueue.main.asyncAfter in the Xcode 26.4 + iOS 26.x environment, then it works without any issue.
So what exactly is going on here? I would really appreciate an explanation.