Your missing EventSource implementation for React Native! React-Native-SSE library supports TypeScript.
We use XMLHttpRequest to establish and handle an SSE connection, so you don't need an additional native Android and iOS implementation. It's easy, just install it with your favorite package manager:
yarn add react-native-ssenpm install --save react-native-sseWe are using Server-Sent Events as a convenient way of establishing and handling Mercure connections. It helps us keep data always up-to-date, synchronize data between devices, and improve real-time workflow. Here you have some usage examples:
import EventSource from "react-native-sse";import EventSource from "react-native-sse";
const es = new EventSource("https://your-sse-server.com/.well-known/mercure");
es.addEventListener("open", (event) => {
console.log("Open SSE connection.");
});
es.addEventListener("message", (event) => {
console.log("New message event:", event.data);
});
es.addEventListener("error", (event) => {
if (event.type === "error") {
console.error("Connection error:", event.message);
} else if (event.type === "exception") {
console.error("Error:", event.message, event.error);
}
});
es.addEventListener("close", (event) => {
console.log("Close SSE connection.");
});If you want to use Bearer token and/or topics, look at this example (TypeScript):
import React, { useEffect, useState } from "react";
import { View, Text } from "react-native";
import EventSource, { EventSourceListener } from "react-native-sse";
import "react-native-url-polyfill/auto"; // Use URL polyfill in React Native
interface Book {
id: number;
title: string;
isbn: string;
}
const token = "[my-hub-token]";
const BookList: React.FC = () => {
const [books, setBooks] = useState<Book[]>([]);
useEffect(() => {
const url = new URL("https://your-sse-server.com/.well-known/mercure");
url.searchParams.append("topic", "/book/{bookId}");
const es = new EventSource(url, {
headers: {
Authorization: {
toString: function () {
return "Bearer " + token;
},
},
},
});
const listener: EventSourceListener = (event) => {
if (event.type === "open") {
console.log("Open SSE connection.");
} else if (event.type === "message") {
const book = JSON.parse(event.data) as Book;
setBooks((prevBooks) => [...prevBooks, book]);
console.log(`Received book ${book.title}, ISBN: ${book.isbn}`);
} else if (event.type === "error") {
console.error("Connection error:", event.message);
} else if (event.type === "exception") {
console.error("Error:", event.message, event.error);
}
};
es.addEventListener("open", listener);
es.addEventListener("message", listener);
es.addEventListener("error", listener);
return () => {
es.removeAllEventListeners();
es.close();
};
}, []);
return (
<View>
{books.map((book) => (
<View key={`book-${book.id}`}>
<Text>{book.title}</Text>
<Text>ISBN: {book.isbn}</Text>
</View>
))}
</View>
);
};
export default BookList;Since the listener is a closure it has access only to the component values from the first render. Each subsequent render has no effect on already defined listeners.
If you use Redux you can get the actual value directly from the store instance.
// full example: https://snack.expo.dev/@quiknull/react-native-sse-redux-example
const Example: React.FC = () => {
const userName = useSelector((state: RootState) => state.user.name);
const pingHandler: EventSourceListener = useCallback(
(event) => {
// In Event Source Listeners in connection with redux
// you should read state directly from store object.
console.log("User name from component selector: ", userName); // bad
console.log("User name directly from store: ", store.getState().user.name); // good
},
[userName]
);
useEffect(() => {
const token = "myToken";
const url = new URL("https://demo.mercure.rocks/.well-known/mercure");
url.searchParams.append(
"topic",
"https://example.com/my-private-topic"
);
const es = new EventSource(url, {
headers: {
Authorization: {
toString: function () {
return "Bearer " + token;
}
}
}
});
es.addEventListener("ping", pingHandler);
}, []);
};new EventSource(url: string | URL, options?: EventSourceOptions);const options: EventSourceOptions = {
method: 'GET'; // Request method. Default: GET
timeout: 0; // Time after which the connection will expire without any activity: Default: 0 (no timeout)
timeoutBeforeConnection: 500; // Time to wait before initial connection is made: Default: 500ms
headers: {}; // Your request headers. Default: {}
body: undefined; // Your request body sent on connection: Default: undefined
debug: false; // Show console.debug messages for debugging purpose. Default: false
pollingInterval: 5000; // Time (ms) between reconnections. Default: 5000
}Using EventSource you can handle custom events invoked by the server:
import EventSource from "react-native-sse";
type MyCustomEvents = "ping" | "clientConnected" | "clientDisconnected";
const es = new EventSource<MyCustomEvents>(
"https://your-sse-server.com/.well-known/hub"
);
es.addEventListener("open", (event) => {
console.log("Open SSE connection.");
});
es.addEventListener("ping", (event) => {
console.log("Received ping with data:", event.data);
});
es.addEventListener("clientConnected", (event) => {
console.log("Client connected:", event.data);
});
es.addEventListener("clientDisconnected", (event) => {
console.log("Client disconnected:", event.data);
});Custom events always emit result with following interface:
export interface CustomEvent<E extends string> {
type: E;
data: string | null;
lastEventId: string | null;
url: string;
}If you see our library is not working properly, feel free to open an issue or create a pull request with your fixes.
The MIT License
Copyright (c) 2021 Binary Minds
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THE SOFTWARE.
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