Use an default WKWebView save all caches, cookies data in the app. So it make very critical issue such as infinite increase app size.

Clean web data in WKWebView

    ///  In AppDelegate.swift
    ///  Execute remove webdata method when the app receives the memory warning.
    ///
    ///  We can not avoid the infinitely get increased the app size issue
    ///  when users keep the web searching using the WKWebView.
    ///  So, you would get iOS full storage message.
    ///
    ///  Set WKWebsiteDataStore.nonPersistentDataStore in the configuration
    ///  can make lightweight WKWebView. But it can not apply every web site.
    ///  Imagine the web sites used the localStorage, IndexedDB features.
    ///
    ///  - parameter application: application
    func applicationDidReceiveMemoryWarning(application: UIApplication) {

        #if DEBUG

            print("memory warning...execute remove webviewdata")

        #endif
        removeWebData()
    }

    /// Remove web data saved in the app, such as caches, cookies.
    func removeWebData() {

        if #available(iOS 9.0, *) {

            let websiteDataTypes = WKWebsiteDataStore.allWebsiteDataTypes()
            let date = NSDate(timeIntervalSince1970: 0)

            WKWebsiteDataStore.defaultDataStore().removeDataOfTypes(websiteDataTypes, modifiedSince: date, completionHandler: {
                #if DEBUG

                    print("remove all data in iOS9 later")

                #endif
            })

        }else {

            // Remove the basic cache.
            NSURLCache.sharedURLCache().removeAllCachedResponses()

            // Delete system cookie store in the app
            let storage = NSHTTPCookieStorage.sharedHTTPCookieStorage()
            if let cookies = storage.cookies {
                for cookie in cookies {
                    storage.deleteCookie(cookie)
                }
            }


            do {
                // folder 를 삭제하는 대신 contents 를 삭제하는 이유?
                // MainVC 가 호출되면 cache, cookie가 발생하므로 로딩시 확인된 cache, cookie 폴더의
                // contents 에 대해서만 삭제 진행.

                // Clear web cache
                try deleteLibraryFolderContents("Caches")

                // Remove all cookies stored by the site. This includes localStorage, sessionStorage, and WebSQL/IndexedDB.
                try deleteLibraryFolderContents("Cookies")

                // Removes all app cache storage.
                try deleteLibraryFolder("WebKit")

            } catch {
                #if DEBUG

                    print("Delete library folders error in iOS9 below")

                #endif

            }
        }
    }

    /**
     Delete folder in library

     - parameter folder: a folder you want to delete

     - throws: throws an error
     */
    func deleteLibraryFolder(folder: String) throws {
        let manager = NSFileManager.defaultManager()
        let library = manager.URLsForDirectory(.LibraryDirectory, inDomains: .UserDomainMask).first!
        let dir = library.URLByAppendingPathComponent(folder)
        try manager.removeItemAtURL(dir)
    }

    /**
     Delete contents in library folder

     - parameter folder: target folder

     - throws: throws an error
     */
    private func deleteLibraryFolderContents(folder: String) throws {
        let manager = NSFileManager.defaultManager()
        let library = manager.URLsForDirectory(NSSearchPathDirectory.LibraryDirectory, inDomains: .UserDomainMask)[0]
        let dir = library.URLByAppendingPathComponent(folder)
        let contents = try manager.contentsOfDirectoryAtPath(dir.path!)
        for content in contents {
            do {
                try manager.removeItemAtURL(dir.URLByAppendingPathComponent(content))
            } catch where ((error as NSError).userInfo[NSUnderlyingErrorKey] as? NSError)?.code == Int(EPERM) {
                // "EPERM: operation is not permitted". We ignore this.
                #if DEBUG

                    print("Couldn't delete some library contents.")

                #endif
            }
        }
    }

Thanks

Dear dakeshi,
You got some great knowledge on WKWebView! I'm trying to load one single WKWebview on the background in my whole app.
When my iOS app opens the a ViewController with it's own class, with 2 textfields and a login button. When the button is pressed, it will fill in the loginform on WKWebView and login.
Then I need to go to the Second viewcontroller with it's OWN class without loding the WKWebView session.
I want to keep the same WKWebView that is logged in. Is it possible to keep the same WKwebview session in more classes?
I don't know How to implement WKProcessPool, could this be a fix?

Is it possible to load a wkwebview in a Classic that can be accessed from anywhere:
Class webviewclass {
var webView = WKWebView()
...
...
init(websiteurl: String()){

}
}
Could you please help me.