Outbound WebSockets

Opening a WebSocket connection for real-time, bi-directional communication with Deno is very simple.

First we need to use the WebSocket constructor to initiate our connection to an external server

const socket = new WebSocket("ws://localhost:8000");

Before we do anything with the websocket, we should wait to make sure that we are connected. We can do so by listening to the "open" event.

socket.addEventListener("open", () => {

We can read the "ready state" of our instance. This determines if we are able to send messages. The ready state for open should be 1.

  console.log(socket.readyState);

We can now send messages to the server. The messages can be of the type string, ArrayBuffer, Blob, or TypedArray. In this case we will be sending a string

  socket.send("ping");
});

We can handle messages back from the server by listening to the "message" event. We can read the data sent by the server using the data property of the event.

socket.addEventListener("message", (event) => {
  console.log(event.data);
});

Run this example locally using the Deno CLI:

deno run --allow-net https://raw.githubusercontent.com/denoland/deno-docs/main/by-example/websocket.ts

Additional resources: