iOS

In iOS you could use a custom url scheme by implementing shouldStartLoadWithRequest. If I would by example want to change the toolbar's tint color:

ViewController.h

@property (strong, nonatomic) IBOutlet UIToolbar *toolbar;

ViewController.m

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType {

    NSURL *url = request.URL;

    NSString *scheme = [url scheme];



    if ([scheme isEqualToString:@color]) {

        self.toolbar.tintColor = [self colorWithHexString:url.host];

    }



    return YES;

}

Javascript

In javascript you just change window.location, which will launch a fire and forget:

window.location = 'color://' + color;

Just chain your parameters like:

window.location = 'myscheme://param1/' + value1 + '/param2/' + value2;

Just make sure you use encodeURIComponent to encode your parameters (to create a valid url).

More info

Android

In Android you add a javascript interface:

    WebView webView = getWebView();

    webView.loadUrl(http://localhost:8080);

    // must be after loadUrl on lower apis

    webView.addJavascriptInterface(new AndroidBridge(this), AndroidBridge);

...

public class AndroidBridge {



    private MainActivity activity;



    public AndroidBridge(MainActivity activity) {

        this.activity = activity;

    }



    @JavascriptInterface

    public void changeNavbarBackground(String color) throws NoSuchFieldException, IllegalArgumentException, IllegalAccessException {

        Log.i(getClass().getSimpleName(), changeNavbarBackground  + color);



        Field f = R.color.class.getField(color);

        final int col = (Integer) f.get(null);



        activity.changeNavbarBackground(col);

    }

}

Javascript

In javascript you use the javascript interface:

if (window.AndroidBridge) {

            window.AndroidBridge.changeNavbarBackground(color);

}