Open Radar

 
Area:
WebKit

Summary:
When loading an HTML page with embedded javascript code, that creates an 'XMLHttpRequest' and uses it to load another resource ,for example a CSV file, the 'onreadystatechange' method of the 'XMLHttpRequest' silently fails on iOS12 when the WKWebview is not attached to the view hierarchy.

I'm including a test project with just the WKWebview, I Also host the relevant HTML page on my server, and also included it and a sample CSV file in the project directory included.

When the project is run, only a few messages will be printed in Xcode terminal, however, if you uncomment line 31 in ViewController.m '[self.view addSubview:self.logicWebView];' you can then see that more logs are being printed, this is because once the WKWebview is added to the view hierarchy 'onreadystatechange' is actually called.

Steps to Reproduce:
1. Create a WKWebview, do not attach it to the view hierarchy.
2. Load a test page that uses an 'XMLHttpRequest' to load a resource.
3. implement 'onreadystatechange' in the test page.
4. try to use 'window.webkit.messageHandlers' to send a message to the client on state change, the message will not be received.


Expected Results:
'onreadystatechange' should work regardless of whether the WKWebview is attached to the view hierarchy or not, as in previous iOS builds.

Actual Results:
'onreadystatechange' is never called on iOS12 when the WKWebview is not attached to the view hierarchy.

Version/Build:
iOS 12 beta 3,4,5.