Cordova 6 app cannot load from file:// path

EDIT:

The ionic team has been working on a fork of the WKWebViewEngine plugin and has fixed some of the XHR issues, not sure if this one is fixed. You can take a look on https://github.com/driftyco/cordova-plugin-wkwebview-engine

Old answer: This is a known issue, local file:// url XmlHttpRequests are not allowed in WKWebViewEngine (https://issues.apache.org/jira/browse/CB-10143)

For more known issues see https://issues.apache.org/jira/browse/CB-10237?jql=labels%20%3D%20wkwebview-known-issues

If you want to make local ajax call to work you should use the wkwebview-engine-localhost plugin (https://github.com/apache/cordova-plugins/tree/master/wkwebview-engine-localhost)

Or Telerik's WKWebView plugin (https://github.com/Telerik-Verified-Plugins/WKWebView).

Both of them will use a local webserver that solves some of the known WKWebView limitations.