本文介绍websocket实现前端通讯
要实现通讯需要连接、发送、接收以及需要websocket服务器

我们来看一个简单的websocket demo

  var socket = new WebSocket('ws://localhost:8080/');
  socket.onopen = function () {
      console.log('Connected!');
  };
  socket.onmessage = function (event) {
      console.log('Received data: ' + event.data);
      socket.close();
  };
  socket.onclose = function () {
      console.log('Lost connection!');
  };
  socket.onerror = function () {
      console.log('Error!');
  };
  socket.send('hello, world!');

可以说上面就是一个健全的websocket 通信了. 我们需要创建一个WebSocket对象, 里面的参数指定连接的路由. 而且，他也是事件驱动的.常见的事件监听有.

websocket 发送数据
另外，websocket 最大的特点就是可以双向通信。这里可以使用.ws.send()
方法发送数据, 不过只能发送String和二进制. 这里，我们通常call 数据叫做 Frames
. 他是数据发送的最小单元.包含数据的长度和数据内容.下面就是几种常用的发送方式

 socket.send("Hello server!"); 
 socket.send(JSON.stringify({'msg': 'payload'})); 

  var buffer = new ArrayBuffer(128);
  socket.send(buffer); 

  var intview = new Uint32Array(buffer);
  socket.send(intview); 

  var blob = new Blob([buffer]);
  socket.send(blob);

另外还可以使用binaryType指定传输的数据格式,不过一般都用不上，就不说了.不过需要提醒的是, send方法，一般在open和message的回调函数中调用.

websocket 接受数据
同理，和SSE差不多, 通过监听message事件，来接受server发送回来的数据. 接受其实就是通过event.data
来获取. 不过, 需要和server端商量好data的类型.

ws.onmessage = function(msg) { 
  if(msg.data instanceof Blob) { 
    processBlob(msg.data);
  } else {
    processText(JSON.parse(msg.data)); //接受JSON数据
  }
}

那server端应该怎样处理websocket通信呢？ websocket虽然是另外一种协议，不过底层还是封装了TCP通信, 所以使用nodeJS的net模块，基本就可以满足，不过里面需要设置很多的头. 这里推荐使用ws模块.
NodeJS 发送websocket数据
简单的websocket demo

var WebSocketServer = require('ws').Server
  , wss = new WebSocketServer({ port: 8080 });

//通过ws+ssl的方式通信. 和HTTPS类似
wss.on('connection', function connection(ws) {
  ws.on('message', function incoming(message) {
    console.log('received: %s', message);
  });

  ws.send('something');
});

具体代码示例：

html

<div id="page-wrapper">
  <h1>WebSockets Demo</h1>
  
  <div id="status">Connecting...</div>
  
  <ul id="messages"></ul>
  
  <form id="message-form" action="#" method="post">
    <textarea id="message" placeholder="Write your message here..." required></textarea>
    <button type="submit">Send Message</button>
    <button type="button" id="close">Close Connection</button>
  </form>
</div>

css

*, *:before, *:after {
  -moz-box-sizing: border-box;
  -webkit-box-sizing: border-box;
  box-sizing: border-box;
}

html {
  font-family: Helvetica, Arial, sans-serif;
  font-size: 100%;
  background: #333;
}

#page-wrapper {
  width: 650px;
  background: #FFF;
  padding: 1em;
  margin: 1em auto;
  border-top: 5px solid #69c773;
  box-shadow: 0 2px 10px rgba(0,0,0,0.8);
}

h1 {
    margin-top: 0;
}

#status {
  font-size: 0.9rem;
  margin-bottom: 1rem;
}

.open {
  color: green;
}

.closed {
  color: red;
}


ul {
  list-style: none;
  margin: 0;
  padding: 0;
  font-size: 0.95rem;
}

ul li {
  padding: 0.5rem 0.75rem;
  border-bottom: 1px solid #EEE;
}

ul li:first-child {
  border-top: 1px solid #EEE;
}

ul li span {
  display: inline-block;
  width: 90px;
  font-weight: bold;
  color: #999;
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 1px;
}

.sent {
  background-color: #F7F7F7;
}

.received {}

#message-form {
  margin-top: 1.5rem;
}

textarea {
  width: 100%;
  padding: 0.5rem;
  font-size: 1rem;
  border: 1px solid #D9D9D9;
  border-radius: 3px;
  box-shadow: inset 0 1px 1px rgba(0, 0, 0, 0.1);
  min-height: 100px;
  margin-bottom: 1rem;
}

button {
  display: inline-block;
  border-radius: 3px;
  border: none;
  font-size: 0.9rem;
  padding: 0.6rem 1em;
  color: white;
  margin: 0 0.25rem;
  text-align: center;
  background: #BABABA;
  border-bottom: 1px solid #999;
}

button[type="submit"] {
  background: #86b32d;
  border-bottom: 1px solid #5d7d1f;
}

button:hover {
  opacity: 0.75;
  cursor: pointer;
}

JS

window.onload = function() {

  // Get references to elements on the page.
  var form = document.getElementById('message-form');
  var messageField = document.getElementById('message');
  var messagesList = document.getElementById('messages');
  var socketStatus = document.getElementById('status');
  var closeBtn = document.getElementById('close');


  // Create a new WebSocket.
  var socket = new WebSocket('ws://echo.websocket.org');


  // Handle any errors that occur.
  socket.onerror = function(error) {
    console.log('WebSocket Error: ' + error);
  };


  // Show a connected message when the WebSocket is opened.
  socket.onopen = function(event) {
    socketStatus.innerHTML = 'Connected to: ws://echo.websocket.org';
    socketStatus.className = 'open';
  };


  // Handle messages sent by the server.
  socket.onmessage = function(event) {
    var message = event.data;
    messagesList.innerHTML += '<li class="received"><span>Received:</span>' +
                               message + '</li>';
  };


  // Show a disconnected message when the WebSocket is closed.
  socket.onclose = function(event) {
    socketStatus.innerHTML = 'Disconnected from WebSocket.';
    socketStatus.className = 'closed';
  };


  // Send a message when the form is submitted.
  form.onsubmit = function(e) {
    e.preventDefault();

    // Retrieve the message from the textarea.
    var message = messageField.value;

    // Send the message through the WebSocket.
    socket.send(message);

    // Add the message to the messages list.
    messagesList.innerHTML += '<li class="sent"><span>Sent:</span>' + message +
                              '</li>';

    // Clear out the message field.
    messageField.value = '';

    return false;
  };


  // Close the WebSocket connection when the close button is clicked.
  closeBtn.onclick = function(e) {
    e.preventDefault();

    // Close the WebSocket.
    socket.close();

    return false;
  };

};

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参考及更多ajax、JSOP、SSE实现前端通讯请阅读
https://segmentfault.com/a/1190000004682473#articleHeader8