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How To Define a Portal API

One of the biggest benefits of including Ionic Portals in an application is the ability to easily communicate between web and native code using the PortalsPlugin. However, to make the integration between a Portal and your native application more seamless, creating your own Plugins may be necessary. By creating a Capacitor Plugin, you can create your own API to communicate between web and native code.

In this example, we will create a plugin that performs a fade-in animation when a Portal has finished loading.

Creating the API Definition

We strongly recommend using TypeScript to create a type definition file which can be used to define your API. This way, there is a central source of truth for the API across Android and iOS as well as having type definitions for web code.

export interface PortalLoadedPlugin {
portalLoaded(): Promise<void>

On the iOS side, the PortalLoadedPlugin class will have to implement a method that matches this type signature.

Implementing the API

class PortalLoadedPlugin: CAPInstancePlugin {
let onPortalLoaded: () -> Void

init(onPortalLoaded: @escaping () -> Void) {
self.onPortalLoaded = onPortalLoaded

@objc func portalLoaded(_ call: CAPPluginCall) {

You'll also need a file called PortalLoadedPlugin.m to create Objective-C bindings through helper macros that Capacitor provides. Below is an example PortalLoadedPlugin Objective-C bindings:

#import <Capacitor/Capacitor.h>

CAP_PLUGIN(PortalLoadedPlugin, "PortalLoadedPlugin",
CAP_PLUGIN_METHOD(portalLoaded, CAPPluginReturnNone);

Using the PortalLoadedPlugin

To use the PortalLoadedPlugin class, we need to create an instance of it and add it to the portal to be rendered. In our example, we'll fade the view in over half a second to ease the transition so we don't get an initial page flash when the portal is rendered.

import UIKit
import IonicPortals

class PortalViewController: UIViewController {
// Create an instance of PortalLoadedPlugin to fade-in the
// portal when our method has been called.
lazy var loadedPlugin = PortalLoadedPlugin { [weak self] in
DispatchQueue.main.async {
UIView.animate(withDuration: 0.5) {
self?.portalView.alpha = 1.0

// Create the PortalUIView by passing in our portal with the
// instance of `PortalLoadedPlugin` added
lazy var portalView: PortalUIView = {
let portalView = PortalUIView(
portal: Portal(name: "foo")

portalView.alpha = 0
return portalView

// Add portalView to the view hierarchy
override func viewDidLoad() {
portalView.translatesAutoresizingMasksIntoConstraints = false
portalView.topAnchor.constraint(equalTo: view.topAnchor),
portalView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
portalView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
portalView.leadingAnchor.constraint(equalTo: view.leadingAnchor),

Calling the Plugin Code from the Web

Once the Plugin has been defined, implemented, and initialized in the native code, it will also need to be registered on the web.

import { registerPlugin } from '@capacitor/core';
import { PortalLoadedPlugin } from '../definitions';

const PortalLoaded = registerPlugin<PortalLoadedPlugin>('PortalLoaded', {
// We create a no-op on the web for development purposes. This no-op plugin will only be loaded when running the plugin
// in a browser during development like Chrome or Safari.
web: { portalLoaded: () -> {} },

export const portalLoaded = () => {
const onPageLoad = async () => {

// Check if the page has already loaded
if (document.readyState === 'complete') {
} else {
window.addEventListener('load', onPageLoad);
export { portalLoaded } from './PortalLoadedPlugin';
export * from './definitions';

This code is not directly exposing the initialized PortalLoaded class outside of the module. In this scenario, we don't want the method triggered for any reason other than when the page is loaded, so we guard that method behind a pure web implementation. If the web code was not needed, we would have just exported this plugin instance directly.

Then, call the method at the start of the web application:

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
import { portalLoaded } from './PortalLoadedPlugin'




For more information on how to create Capacitor Plugins, check our guide for creating Capacitor Plugins.