Using WKWebview to get userAgent synchronously

UserAgentFetcher.swift

public final class UserAgentFetcher: NSObject {
    
    private let webView: WKWebView = WKWebView(frame: .zero)
    
    @objc
    public func fetch() -> String {
        dispatchPrecondition(condition: .onQueue(.main))

        var result: String?
        
        webView.evaluateJavaScript("navigator.userAgent") { response, error in
            if let error = error {
                result = ""
                return
            }
            
            result = response as? String ?? ""
        }

        while (result == nil) {
            RunLoop.main.run(until: Date(timeIntervalSinceNow: 0.01))
        }

        return result ?? ""
    }
    
}