WKWebView function for detecting if the URL has changed

You may add an observer:

[webView_ addObserver:self forKeyPath:@"URL" options:NSKeyValueObservingOptionNew context:NULL];

and the corresponding method that gets called when the URL changes:

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context

What do you mean they don't always seem to fire? What kind of elements? They have to in order for the WkWebView to work.

Your first indication that the URL is trying to change is in: decidePolicyForNavigationAction

- (void) webView: (WKWebView *) webView decidePolicyForNavigationAction: (WKNavigationAction *) navigationAction decisionHandler: (void (^)(WKNavigationActionPolicy)) decisionHandler {
    NSLog(@"%s", __PRETTY_FUNCTION__);
    decisionHandler(WKNavigationActionPolicyAllow); //Always allow
    NSURL *u1 = webView.URL;
    NSURL *u2 = navigationAction.request.URL; //If changing URLs this one will be different
}

By the time you get to: didStartProvisionalNavigation It has changed.

- (void) webView: (WKWebView *) webView didStartProvisionalNavigation: (WKNavigation *) navigation {
    NSLog(@"%s", __PRETTY_FUNCTION__);
    NSURL *u1 = webView.URL;  //By this time it's changed
}

All you'd have to do is implement these delegate methods (in Swift) and do what you want when you see it change.

Swift Version

// Add observer
webView.addObserver(self, forKeyPath: "URL", options: .new, context: nil)

// Observe value
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if let key = change?[NSKeyValueChangeKey.newKey] {
        print("observeValue \(key)") // url value
    }
}