1# WebSocket Connection 2 3## When to Use 4 5You can use WebSocket to establish a bidirectional connection between a server and a client. Before doing this, you need to use the **createWebSocket()** API to create a **WebSocket** object and then use the **connect()** API to connect to the server. 6If the connection is successful, the client will receive a callback of the **open** event. Then, the client can communicate with the server using the **send()** API. 7When the server sends a message to the client, the client will receive a callback of the **message** event. If the client no longer needs this connection, it can call the **close()** API to disconnect from the server. Then, the client will receive a callback of the **close** event. 8 9If an error occurs in any of the preceding processes, the client will receive a callback of the **error** event. 10 11## Available APIs 12 13The WebSocket connection function is mainly implemented by the WebSocket module. To use related APIs, you must declare the **ohos.permission.INTERNET** permission. The following table describes the related APIs. 14 15| API| Description| 16| -------- | -------- | 17| createWebSocket() | Creates a WebSocket connection.| 18| connect() | Establishes a WebSocket connection to a given URL.| 19| send() | Sends data through the WebSocket connection.| 20| close() | Closes a WebSocket connection.| 21| on(type: 'open') | Enables listening for **open** events of a WebSocket connection.| 22| off(type: 'open') | Disables listening for **open** events of a WebSocket connection.| 23| on(type: 'message') | Enables listening for **message** events of a WebSocket connection.| 24| off(type: 'message') | Disables listening for **message** events of a WebSocket connection.| 25| on(type: 'close') | Enables listening for **close** events of a WebSocket connection.| 26| off(type: 'close') | Disables listening for **close** events of a WebSocket connection.| 27| on(type: 'error') | Enables listening for **error** events of a WebSocket connection.| 28| off(type: 'error') | Disables listening for **error** events of a WebSocket connection.| 29 30## How to Develop 31 321. Import the required webSocket module. 33 342. Create a **WebSocket** object. 35 363. (Optional) Subscribe to WebSocket **open**, **message**, **close**, and **error** events. 37 384. Establish a WebSocket connection to a given URL. 39 405. Close the WebSocket connection if it is no longer needed. 41 42```js 43import webSocket from '@ohos.net.webSocket'; 44 45var defaultIpAddress = "ws://"; 46let ws = webSocket.createWebSocket(); 47ws.on('open', (err, value) => { 48 console.log("on open, status:" + JSON.stringify(value)); 49 // When receiving the on('open') event, the client can use the send() API to communicate with the server. 50 ws.send("Hello, server!", (err, value) => { 51 if (!err) { 52 console.log("Message sent successfully"); 53 } else { 54 console.log("Failed to send the message. Err:" + JSON.stringify(err)); 55 } 56 }); 57}); 58ws.on('message', (err, value) => { 59 console.log("on message, message:" + value); 60 // When receiving the `bye` message (the actual message name may differ) from the server, the client proactively disconnects from the server. 61 if (value === 'bye') { 62 ws.close((err, value) => { 63 if (!err) { 64 console.log("Connection closed successfully"); 65 } else { 66 console.log("Failed to close the connection. Err: " + JSON.stringify(err)); 67 } 68 }); 69 } 70}); 71ws.on('close', (err, value) => { 72 console.log("on close, code is " + value.code + ", reason is " + value.reason); 73}); 74ws.on('error', (err) => { 75 console.log("on error, error:" + JSON.stringify(err)); 76}); 77ws.connect(defaultIpAddress, (err, value) => { 78 if (!err) { 79 console.log("Connected successfully"); 80 } else { 81 console.log("Connection failed. Err:" + JSON.stringify(err)); 82 } 83}); 84``` 85