files/en-us/web/api/web-based_payment_handler_api/index.md
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The Web-based Payment Handler API provides a standardized set of functionality for web applications to directly handle payments, rather than having to be redirected to a separate site for payment handling.
When a merchant website initiates payment via the {{domxref("Payment Request API", "Payment Request API", "", "nocode")}}, the Web-based Payment Handler API handles discovery of applicable payment apps, presenting them as choices to the user, opening a payment handler window once a choice has been made to allow the user to enter their payment details, and handling the payment transaction with the payment app.
Communication with payment apps (authorization, passing of payment credentials) is handled via Service Workers.
On a merchant website, a payment request is initiated by the construction of a new {{domxref("PaymentRequest")}} object:
const request = new PaymentRequest(
[
{
supportedMethods: "https://bobbucks.dev/pay",
},
],
{
total: {
label: "total",
amount: { value: "10", currency: "USD" },
},
},
);
The supportedMethods property specifies a URL representing the payment method supported by the merchant. To use more than one payment method, you would specify them in an array of objects, like this:
const request = new PaymentRequest(
[
{
supportedMethods: "https://alicebucks.dev/pay",
},
{
supportedMethods: "https://bobbucks.dev/pay",
},
],
{
total: {
label: "total",
amount: { value: "10", currency: "USD" },
},
},
);
In supporting browsers, the process starts by requesting a payment method manifest file from each URL. A payment method manifest is typically called something like payment-manifest.json (the exact name can be whatever you like), and should be structured like this:
{
"default_applications": ["https://bobbucks.dev/manifest.json"],
"supported_origins": ["https://alicepay.friendsofalice.example"]
}
Given a payment method identifier like https://bobbucks.dev/pay, the browser:
https://bobbucks.dev/pay and checks its HTTP headers.
rel="payment-method-manifest", then it downloads the payment method manifest at that location instead (see Optionally route the browser to find the payment method manifest in another location for details).https://bobbucks.dev/pay as the payment method manifest.default_applications and supported_origins members.These members have the following purposes:
default_applications tells the browser where to find the default payment app that can use the BobBucks payment method if it doesn't already have one installed.supported_origins tells the browser what other payment apps are permitted to handle the BobBucks payment if needed. If they are already installed on the device, they will be presented to the user as alternative payment options alongside the default application.From the payment method manifest, the browser gets the URL of the default payment apps' web app manifest files, which can be called whatever you like, and look something like this:
{
"name": "Pay with BobBucks",
"short_name": "BobBucks",
"description": "This is an example of the Web-based Payment Handler API.",
"icons": [
{
"src": "images/manifest/icon-192x192.png",
"sizes": "192x192",
"type": "image/png"
},
{
"src": "images/manifest/icon-512x512.png",
"sizes": "512x512",
"type": "image/png"
}
],
"serviceworker": {
"src": "service-worker.js",
"scope": "/",
"use_cache": false
},
"start_url": "/",
"display": "standalone",
"theme_color": "#3f51b5",
"background_color": "#3f51b5",
"related_applications": [
{
"platform": "play",
"id": "com.example.android.samplepay",
"min_version": "1",
"fingerprints": [
{
"type": "sha256_cert",
"value": "4C:FC:14:C6:97:DE:66:4E:66:97:50:C0:24:CE:5F:27:00:92:EE:F3:7F:18:B3:DA:77:66:84:CD:9D:E9:D2:CB"
}
]
}
]
}
When the {{domxref("PaymentRequest.show()")}} method is invoked by the merchant app in response to a user gesture, the browser uses the name and icons information found in each manifest to present the payment apps to the user in the browser-provided Payment Request UI.
serviceworker member so it can handle the payment.[!NOTE] If
prefer_related_applicationsis set totruein the payment app manifest, the browser will launch the platform-specific payment app specified inrelated_applicationsto handle the payment (if it is available) instead of the web payment app.
See Serve a web app manifest for more details.
The Payment Request API's {{domxref("PaymentRequest.canMakePayment()")}} method returns true if a payment app is available on the customer's device, meaning that a payment app that supports the payment method is discovered, and that the platform-specific payment app is installed, or the web-based payment app is ready to be registered.
async function checkCanMakePayment() {
// …
const canMakePayment = await request.canMakePayment();
if (!canMakePayment) {
// Fallback to other means of payment or hide the button.
}
}
The Web-based Payment Handler API adds an additional mechanism to prepare for handling a payment. The {{domxref("ServiceWorkerGlobalScope.canmakepayment_event", "canmakepayment")}} event is fired on a payment app's service worker to check whether it is ready to handle a payment. Specifically, it is fired when the merchant website calls the {{domxref("PaymentRequest.PaymentRequest", "PaymentRequest()")}} constructor. The service worker can then use the {{domxref("CanMakePaymentEvent.respondWith()")}} method to respond appropriately:
self.addEventListener("canmakepayment", (e) => {
e.respondWith(
new Promise((resolve, reject) => {
someAppSpecificLogic()
.then((result) => {
resolve(result);
})
.catch((error) => {
reject(error);
});
}),
);
});
The promise returned by respondWith() resolves with a boolean to signal that it is ready to handle a payment request (true), or not (false).
After the {{domxref("PaymentRequest.show()")}} method is invoked, a {{domxref("ServiceWorkerGlobalScope.paymentrequest_event", "paymentrequest")}} event is fired on the service worker of the payment app. This event is listened for inside the payment app's service worker to begin the next stage of the payment process.
let paymentRequestEvent;
let resolver;
let client;
// `self` is the global object in service worker
self.addEventListener("paymentrequest", async (e) => {
if (paymentRequestEvent) {
// If there's an ongoing payment transaction, reject it.
resolver.reject();
}
// Preserve the event for future use
paymentRequestEvent = e;
// …
});
When a paymentrequest event is received, the payment app can open a payment handler window by calling {{domxref("PaymentRequestEvent.openWindow()")}}. The payment handler window will present the customers with a payment app interface where they can authenticate, choose shipping address and options, and authorize the payment.
When the payment has been handled, {{domxref("PaymentRequestEvent.respondWith()")}} is used to pass the payment result back to the merchant website.
See Receive a payment request event from the merchant for more details of this stage.
Once a payment app service worker is registered, you can use the service worker's {{domxref("PaymentManager")}} instance (accessed via {{domxref("ServiceWorkerRegistration.paymentManager")}}) to manage various aspects of the payment app's functionality.
For example:
navigator.serviceWorker.register("serviceworker.js").then((registration) => {
registration.paymentManager.userHint = "Card number should be 16 digits";
registration.paymentManager
.enableDelegations(["shippingAddress", "payerName"])
.then(() => {
// …
});
// …
});
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