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crookedneighbor Update PayPal instructions (#10)
* Update PayPal instructions

* Clarify role of localhost:3099

* Add note about quick start instructions in PayPal instructions
Latest commit 92c7981 May 31, 2018


PopupBridge iOS

PopupBridge is an iOS library that allows WKWebViews to open popup windows in an SFSafariViewController browser and send data back to the parent page in the WKWebView.

PopupBridge is also available for Android.

See the Frequently Asked Questions to learn more about PopupBridge. See Using PayPal in a WebView to use PopupBridge with PayPal.


  • iOS 9.0+


PopupBridge is available through CocoaPods. To install it, add the following line to your Podfile:

pod 'PopupBridge'

To integrate using Carthage, add github "braintree/popup-bridge-ios" to your Cartfile, and add the frameworks to your project.


To run the example app, clone the repo, open PopupBridge.xcworkspace and run the PopupBridge-Example app target.

Quick Start

  1. Register a URL type for your app:

    • In Xcode, click on your project in the Project Navigator and navigate to App Target > Info > URL Types
    • Click [+] to add a new URL type
    • Under URL Schemes, enter a unique URL scheme, e.g. com.my-app.popupbridge
  2. In your application delegate, set up PopupBridge with the URL scheme:

    #import "POPPopupBridge.h"
    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
        [POPPopupBridge setReturnURLScheme:@"com.my-app.popupbridge"];
        return YES;
    - (BOOL)application:(UIApplication *)app
                openURL:(NSURL *)url
                options:(NSDictionary<UIApplicationOpenURLOptionsKey,id> *)options {
        if ([url.scheme localizedCaseInsensitiveCompare:@"com.my-app.popupbridge"] == NSOrderedSame) {
            return [POPPopupBridge openURL:url options:options];
        return NO;
  3. Integrate PopupBridge with the WKWebView:

    #import "POPPopupBridge.h"
    @interface MyViewController () <POPPopupBridgeDelegate>
    @property (nonatomic, strong) WKWebView *webView;
    @property (nonatomic, strong) POPPopupBridge *popupBridge;
    @implementation MyViewController
    - (void)viewDidLoad
        [super viewDidLoad];
        self.webView = [[WKWebView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        [self.view addSubview:self.webView];
        self.popupBridge = [[POPPopupBridge alloc] initWithWebView:self.webView delegate:self];
        // replace http://localhost:3099/ with the webpage you want to open in the webview
        [self.webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://localhost:3099/"]]];
    - (void)popupBridge:(POPPopupBridge *)bridge requestsPresentationOfViewController:(UIViewController *)viewController {
        [self presentViewController:viewController animated:YES completion:nil];
    - (void)popupBridge:(POPPopupBridge *)bridge requestsDismissalOfViewController:(UIViewController *)viewController {
      [viewController dismissViewControllerAnimated:YES completion:nil];
  4. Use PopupBridge from the web page by writing some JavaScript:

    var url = 'http://localhost:3099/popup'; // or whatever the page is that you want to open in a popup
    if (window.popupBridge) {
      // Open the popup in a browser, and give it the deep link back to the app
      popupBridge.open(url + '?popupBridgeReturnUrlPrefix=' + popupBridge.getReturnUrlPrefix());
      // Optional: define a callback to process results of interaction with the popup
      popupBridge.onComplete = function (err, payload) {
        if (err) {
          console.error('PopupBridge onComplete Error:', err);
        } else if (!err && !payload) {
          console.log('User closed popup.');
        } else {
          alert('Your favorite color is ' + payload.queryItems.color);
    } else {
      var popup = window.open(url);
      window.addEventListener('message', function (event) {
        var color = JSON.parse(event.data).color;
        if (color) {
          alert('Your favorite color is ' + color);
  5. Redirect back to the app inside of the popup:

    <h1>What is your favorite color?</h1>
    <a href="#red" data-color="red">Red</a>
    <a href="#green" data-color="green">Green</a>
    <a href="#blue" data-color="blue">Blue</a>
    <script src="jquery.js"></script>
    $('a').on('click', function (event) {
      var color = $(this).data('color');
      if (location.search.indexOf('popupBridgeReturnUrlPrefix') !== -1) {
        var prefix = location.search.split('popupBridgeReturnUrlPrefix=')[1];
        // Open the deep link back to the app, and send some data
        location.href = prefix + '?color=' + color;
      } else {
        window.opener.postMessage(JSON.stringify({ color: color }), '*');

Frequently Asked Questions

Why use PopupBridge?

WKWebView can open popups through its WKUIDelegate, which can be implemented to present the popup in a new WKWebView.

However, WKWebViews do not display an address bar or an HTTPS lock icon. If the popup receives sensitive user information (e.g. login credentials), users must implicitly trust that the web page is not redirecting them to a malicious spoofed page that may steal their information. PopupBridge solves this by using an SFSafariViewController.

What are some use cases for using PopupBridge?

  • Apps with WebViews that need to open a popup
  • When a popup window needs to to send data from the popup back to the WKWebView
  • When the popup window needs to display the HTTPS lock icon to increase user trust
  • Apps that use OAuth

How does it work?

  • PopupBridge attaches to a WKWebView by injecting a user script to the page
    • This exposes a JavaScript interface (via window.popupBridge) for the web page to interact with the iOS code
  • The web page detects whether the page has access to window.popupBridge; if so, it uses popupBridge.open to open the popup URL
    • popupBridge.open creates a SFSafariViewController to open the popup URL and has its delegate present the view controller
    • The web page can also use popupBridge.onComplete as a callback
  • The popup web page uses a deep link URL to dismiss the popup
    • The deep link URL should match a deep link URL type in Xcode

    • The app delegate handles the deep link URL and forwards it to PopupBridge

    • One way to avoid hard-coding the deep link is by adding it as a query parameter to the popup URL:

        popupBridge.open(url + '?popupBridgeReturnUrlPrefix=' + popupBridge.getReturnUrlPrefix());
      • Optionally, you can add path components and query parameters to the deep link URL to return data to the parent page, which are provided in the payload of popupBridge.onComplete
  • If the user taps the Done button on the SFSafariViewController, popupBridge.onComplete gets called with the error and payload as null and the delegate dismisses the view controller

Who built PopupBridge?

We are engineers who work on the Developer Experience team at Braintree.

Why did Braintree build PopupBridge?

Short answer: to accept PayPal as a payment option when mobile apps are using a WebView to power the checkout process.

PayPal authentication occurs in a popup window. However, this causes issues with Braintree merchants who use a web page to power payments within their apps: they can't accept PayPal because WebViews cannot open popups and return the PayPal payment authorization data to the parent checkout page.

PopupBridge solves this problem by allowing braintree-web or PayPal's Checkout.js to open the PayPal popup from a secure mini-browser.

Using PayPal in a WebView

WebView-based checkout flows can accept PayPal with PopupBridge and the Braintree JS SDK or PayPal's Checkout.js. For the authentication flow, PayPal requires a popup window—which can be simulated with PopupBridge.


  1. Create a web-based checkout that accepts PayPal using Checkout.js or the Braintree JS SDK
  2. Create a native mobile app that opens the checkout in a WKWebView (See steps 1-3 of the quick start instructions)
  3. Integrate the PopupBridge library
  4. Collect device data
    • To help detect fraudulent activity, collect device data before performing PayPal transactions. This is similar to collecting device data with our native iOS SDK with a few differences:
      1. Rather than importing the entire data collector, you can add just PayPalDataCollector to your app: pod 'Braintree/PayPalDataCollector'
      2. Implement methods in your native app depending on whether you are doing one-time payments or vaulted payments. See the iOS code snippets for PayPal + PopupBridge
  5. Profit!


Braintree, code@getbraintree.com


PopupBridge is available under the MIT license. See the LICENSE file for more info.