In Safari V9.0.3 (10601.4.4), neither then() nor catch() is called when a request timeout occurs. Instead, Safari prints out the following error to the console:

In Chrome V49.0.2623.87 (64-bit), the catch() callback is properly executes as expected.

Test Script Used:

fetch('http://10.255.255.1') // a non-routable IP address
    .then(function(response) {
        console.log("response.ok", response.ok);
    }).catch(function(error) {
        console.log('Failed: ', error)
    });

Without either then() or catch() being called on timeout, how are we supposed to handle this type of request failure for Safari browsers?