Transports

The bridge picks a transport per call, in order: Android, iOS, React Native, web.

Outgoing

Platform	Detection	Call
Android WebView	window.AndroidBridge	AndroidBridge[method](JSON.stringify(props))
iOS WebView	window.webkit.messageHandlers.VKWebAppClose	webkit.messageHandlers[method].postMessage(props)
React Native	window.ReactNativeWebView.postMessage	postMessage(JSON.stringify({ handler: method, params: props }))
Web (iframe in a host)	anything else, given a window	parent.postMessage(envelope, "*")

The web envelope’s shape is part of the platform contract:

parent.postMessage(
    {
        handler: "VKWebAppGetUserInfo",
        params: { request_id: "__vkma_1" },
        type: "vk-connect",
        webFrameId: "frame-1", // assigned by the host, see below
        connectVersion: "0.1.0", // the version from createVKBridge
    },
    "*",
);

The "*" targetOrigin is constant: a mini app cannot know the host origin ahead of time (vk.ru, m.vk.ru, mobile clients).

Incoming

• Web: the message event on window, body { type, data, frameId }.
• Android and iOS WebViews: the native layer dispatches ready-made CustomEvent("VKWebAppEvent") on window.
• React Native on Android: message on document; RN delivers a JSON string — the bridge parses it and processes it like a web envelope.

The VKWebAppSettings event is internal protocol: the host assigns the iframe its webFrameId, the bridge remembers it and puts it into every outgoing envelope. It is never delivered to subscribers.

Lazy host detection

Transports read window.AndroidBridge / webkit.messageHandlers / parent on every call instead of caching them at import time: a fake host can be installed at any point in a unit test, and the next call picks it up.

supportsAsync

Support detection depends on the environment:

• Android and iOS WebViews probe the native objects synchronously: an AndroidBridge[method] or messageHandlers[method] that exists means the method is supported.
• Web sends SetSupportedHandlers once and caches the answer; repeat SetSupportedHandlers pushes from the host refresh the cache. On error or an empty answer the fallback is a set of one: VKWebAppInit.

if (await bridge.supportsAsync("VKWebAppShowStoryBox")) {
    await bridge.send("VKWebAppShowStoryBox", props);
}

Environment

A family of synchronous checks on the instance:

• isWebView() — iOS or Android WebView;
• isIframe() — window.parent !== window;
• isEmbedded() — webview or iframe, i.e. the app runs inside a host;
• isStandalone() — the opposite: opened outside any host.

Environment checks do not replace supportsAsync: a method can exist on the platform yet be unavailable in a particular client.