You can define your async func like this extension WKWebView {         @discardableResult     func evaluateJavaScriptAsync(_ str: String) async throws -> Any? {         return try await withCheckedThrowingContinuation { (continuation: CheckedContinuation<Any?, Error>) in             DispatchQueue.main.async {                 self.evaluateJavaScript(str) { data, error in                     if let error = error {                         continuation.resume(throwing: error)                     } else {                         continuation.resume(returning: data)                     }                 }             }         }     } }

This worked for me. didEndDisplaying denotes collectionView is now ready to scroll firstTimeScrollClosure = { collectionView.scrollToItem(at: indexPath, at: .centeredHorizontally, animated: false) } func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {         firstTimeScrollClosure?()         firstTimeScrollClosure = nil }

I did custom implement that auto-fill feature, would like to share use it with let data = AutoFillData(fName: "Jhon") webView.evaluateJavaScript(data.createJSString(), completionHandler: nil) It searches dom elements with name and id struct AutoFillData {     var fName: String?     var lName: String?     var email: String?     var phone: String?     var shipAddress: String?     var shipCity: String?     var shipState: String?     var shipCountry: String?     var zip: String?     enum KeyNames: String, CaseIterable {         case first_name, customerFirstName,              last_name, customerLastName,              name,              email, customerEmail,              phone, alternatePhone, phoneNumber, phoneNumber2 = "phone-number",              shipAddress = "ship-address", addressLine1, addressLine2,              shipCity = "ship-city", city,              shipState = "ship-state", state,              shipZip = "ship-zip", zip, pincode,              shipCountry = "ship-country", country     }     func getData(keyName: KeyNames) -> String? {         switch keyName {         case .first_name, .customerFirstName: return fName         case .last_name, .customerLastName: return lName         case .name: return [fName, lName].compactMap { $0 }.joined(separator: " ")         case .email, .customerEmail: return email         case .phone, .alternatePhone, .phoneNumber, .phoneNumber2: return phone         case .shipAddress, .addressLine1, .addressLine2: return shipAddress         case .shipCity, .city: return shipCity         case .shipState, .state: return shipState         case .shipCountry, .country: return shipCountry         case .zip, .shipZip, .pincode: return zip         }     }     func createJSString() -> String {         var str = ""         KeyNames.allCases.forEach {             let value = getData(keyName: $0)?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""             if !value.isEmpty {                 str.append("""                 var e = document.getElementsByName('\($0.rawValue)')[0];                 if (e == null) {                     e = document.getElementById('\($0.rawValue)');                 }                 if (e != null) {                     e.value = '\(value)';                 }                 """)             }         }         return str     } }