众所周知传统的http协议是客户端（浏览器）发送请求，浏览器响应请求的方式，一条请求对应一条响应。若浏览器不主动请求则服务端无法想客户端主动推数据。传统的方式是使用AJAX轮询（这个方式有它的问题）来解决这一问题后面展开讲。

应用场景

列举几个应用场景：

• 网络聊天室

• 多人在线游戏

• 网站向页面实时推送广告、消息

• 在线实现对控制设备的控制

前面三个应用场景已经有很多大佬讲过了，我就不讲了，这里主要简单分析一下第四个应用场景。

场景4：

家里装有“XX”牌网络摄像机，我现在工作想看看自家“二哈”有没有在拆家,打开改公司提供的app查看家里的情况，很不巧相机现在没有开机，不过可以通过app控制相机开机，点击开机按钮相机开机。但是相机开机需要一段时间。这时传统的做法是通过AJAX轮询的方式每个1秒左右就向服务器发送请求询问设备是否准备就绪。

客户端> 开机没啊，能不能播放视频了呀。

服务端> 还没呢，别着急等会儿再来。

客户端> 开机没啊，能不能播放视频了呀。

服务端> 还没呢，别着急等会儿再来。

客户端> 开机没啊，能不能播放视频了呀。

服务端> 还没呢，别着急等会儿再来。

......

N次之后

......

客户端> 开机没啊，能不能播放视频了呀。。。

服务端> 可以了，你可以播放了

这个看出客户端要通过很多次询问后，才能知道服务端什么时候准备就绪，这样如果发送请求的客户特别多，请求频率特别高这无疑会给服务端造成了不小的压力。

如果有那么一种方式可以让服务端想客户端推送消息，就可以完美解决这一情况，于是WebSocket出现了。

WebSocket的使用

WebSocket是HTML5的新协议，所以支持HTML5的浏览器都能直接使用WebSocket不需要额外安装，什么开发包，或者插件。

为了测试WebSocket我们需要简单的搞一个服务端程序。Node.js本身支持的协议包括TCP协议和HTTP协议，但不支持WebSocket，为了让让node也支持WebSocket，这里我选用ws模块。

测试

创建一个名为testWebSocket的文件夹，使用npm init 初始化项目

配置package.json文件添加，这里选用ws的最新的版本

<span style="padding-right: 0.1px"><span class="cm-string" style="color: #aa1111">"dependencies"</span>: {</span><br><span style="padding-right: 0.1px"><span class="cm-string cm-property">　　"ws"</span>: <span class="cm-string" style="color: #aa1111">"^6.2.1"</span></span><br><span style="padding-right: 0.1px">}</span>

在根目录使用npm指令npm install --save，把ws相关依赖都拉下来。

然后创建一个名为myWebSocketServer.js的文件，一个简单的WebSocket服务端程序完成，

node myWebSocketServer.js先让服务端跑起来。相关教程：webSocket 视频教程

<span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">// 导入WebSocket模块:</span></span><br><span style="padding-right: 0.1px"><span class="cm-keyword" style="color: #770088">const</span> <span class="cm-def" style="color: #0000ff">WebSocket</span> <span class="cm-operator" style="color: #981a1a">=</span> <span class="cm-variable" style="color: #000000">require</span>(<span class="cm-string" style="color: #aa1111">'ws'</span>);</span><br><span style="padding-right: 0.1px"><span class="cm-keyword" style="color: #770088">let</span> <span class="cm-def" style="color: #0000ff">i</span> <span class="cm-operator" style="color: #981a1a">=</span> <span class="cm-number" style="color: #116644">1</span>;</span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">// 引用Server类:</span></span><br><span style="padding-right: 0.1px"><span class="cm-keyword" style="color: #770088">const</span> <span class="cm-def" style="color: #0000ff">WebSocketServer</span> <span class="cm-operator" style="color: #981a1a">=</span> <span class="cm-variable" style="color: #000000">WebSocket</span>.<span class="cm-property" style="color: #000000">Server</span>;</span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">// 实例化:</span></span><br><span style="padding-right: 0.1px"><span class="cm-keyword" style="color: #770088">const</span> <span class="cm-def" style="color: #0000ff">myWs</span> <span class="cm-operator" style="color: #981a1a">=</span> <span class="cm-keyword" style="color: #770088">new</span> <span class="cm-variable" style="color: #000000">WebSocketServer</span>({</span><br><span style="padding-right: 0.1px">    <span class="cm-property" style="color: #000000">port</span>: <span class="cm-number" style="color: #116644">8080</span></span><br><span style="padding-right: 0.1px">});</span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px"><span class="cm-variable" style="color: #000000">myWs</span>.<span class="cm-property" style="color: #000000">on</span>(<span class="cm-string" style="color: #aa1111">'connection'</span>, <span class="cm-def" style="color: #0000ff">ws</span> <span class="cm-operator" style="color: #981a1a">=></span> {</span><br><span style="padding-right: 0.1px">    <span class="cm-variable-2" style="color: #0055aa">ws</span>.<span class="cm-property" style="color: #000000">on</span>(<span class="cm-string" style="color: #aa1111">'message'</span>, <span class="cm-def" style="color: #0000ff">message</span> <span class="cm-operator" style="color: #981a1a">=></span> {</span><br><span style="padding-right: 0.1px">        <span class="cm-variable" style="color: #000000">console</span>.<span class="cm-property" style="color: #000000">log</span>(<span class="cm-string" style="color: #aa1111">'received: %s'</span>, <span class="cm-variable-2" style="color: #0055aa">message</span>);</span><br><span style="padding-right: 0.1px">    });</span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px">    <span class="cm-variable" style="color: #000000">setInterval</span>(() <span class="cm-operator" style="color: #981a1a">=></span> {</span><br><span style="padding-right: 0.1px">        <span class="cm-variable-2" style="color: #0055aa">ws</span>.<span class="cm-property" style="color: #000000">send</span>(<span class="cm-string" style="color: #aa1111">'Hello siegaii this is serverMessage!'</span> <span class="cm-operator" style="color: #981a1a">+</span> <span class="cm-variable" style="color: #000000">i</span>);</span><br><span style="padding-right: 0.1px">        <span class="cm-variable" style="color: #000000">i</span><span class="cm-operator" style="color: #981a1a">++</span>;</span><br><span style="padding-right: 0.1px">    }, <span class="cm-number" style="color: #116644">1000</span>);</span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px">});</span>

客户端

<span style="padding-right: 0.1px"><span class="cm-meta" style="color: #555555"></span><br><span style="padding-right: 0.1px"><span class="cm-tag cm-bracket" style="color: #117700"><span class="cm-tag" style="color: #117700">html</span> <span class="cm-attribute" style="color: #0000cc">lang</span>=<span class="cm-string" style="color: #aa1111">"en"</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span><br><span style="padding-right: 0.1px"><span class="cm-tag cm-bracket" style="color: #117700"><span class="cm-tag" style="color: #117700">head</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span><br><span style="padding-right: 0.1px">    <span class="cm-tag cm-bracket" style="color: #117700"><span class="cm-tag" style="color: #117700">meta</span> <span class="cm-attribute" style="color: #0000cc">charset</span>=<span class="cm-string" style="color: #aa1111">"UTF-8"</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span><br><span style="padding-right: 0.1px">    <span class="cm-tag cm-bracket" style="color: #117700"><span class="cm-tag" style="color: #117700">title</span><span class="cm-tag cm-bracket" style="color: #117700">></span>test<span class="cm-tag cm-bracket" style="color: #117700"></span><span class="cm-tag" style="color: #117700">title</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span><br><span style="padding-right: 0.1px"><span class="cm-tag cm-bracket" style="color: #117700"></span><span class="cm-tag" style="color: #117700">head</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span><br><span style="padding-right: 0.1px"><span class="cm-tag cm-bracket" style="color: #117700"><span class="cm-tag" style="color: #117700">body</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span><br><span style="padding-right: 0.1px"><span class="cm-tag cm-bracket" style="color: #117700"><span class="cm-tag" style="color: #117700">button</span> <span class="cm-attribute" style="color: #0000cc">id</span>=<span class="cm-string" style="color: #aa1111">"test"</span><span class="cm-tag cm-bracket" style="color: #117700">></span>hello siegaii<span class="cm-tag cm-bracket" style="color: #117700"></span><span class="cm-tag" style="color: #117700">button</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px"><span class="cm-tag cm-bracket" style="color: #117700"><span class="cm-tag" style="color: #117700">script</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span><br><span style="padding-right: 0.1px">    <span class="cm-keyword" style="color: #770088">let</span> <span class="cm-def" style="color: #0000ff">ws</span> <span class="cm-operator" style="color: #981a1a">=</span> <span class="cm-keyword" style="color: #770088">new</span> <span class="cm-variable" style="color: #000000">WebSocket</span>(<span class="cm-string" style="color: #aa1111">'ws://localhost:8080/testWebSocket'</span>);</span><br><span style="padding-right: 0.1px">    <span class="cm-variable" style="color: #000000">document</span>.<span class="cm-property" style="color: #000000">getElementById</span>(<span class="cm-string" style="color: #aa1111">'test'</span>).<span class="cm-property" style="color: #000000">addEventListener</span>(<span class="cm-string" style="color: #aa1111">'click'</span>, () <span class="cm-operator" style="color: #981a1a">=></span> {</span><br><span style="padding-right: 0.1px">        <span class="cm-variable" style="color: #000000">ws</span>.<span class="cm-property" style="color: #000000">send</span>(<span class="cm-string" style="color: #aa1111">'Hello Siegaii this is clientMessage!'</span>);</span><br><span style="padding-right: 0.1px">    });</span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px">    <span class="cm-comment" style="color: #aa5500">// 响应onmessage事件:</span></span><br><span style="padding-right: 0.1px">    <span class="cm-variable" style="color: #000000">ws</span>.<span class="cm-property" style="color: #000000">onmessage</span> <span class="cm-operator" style="color: #981a1a">=</span> (<span class="cm-def" style="color: #0000ff">msg</span>) <span class="cm-operator" style="color: #981a1a">=></span> {</span><br><span style="padding-right: 0.1px">        <span class="cm-variable" style="color: #000000">console</span>.<span class="cm-property" style="color: #000000">log</span>(<span class="cm-variable-2" style="color: #0055aa">msg</span>);</span><br><span style="padding-right: 0.1px">    };</span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px"><span class="cm-tag cm-bracket" style="color: #117700"></span><span class="cm-tag" style="color: #117700">script</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span><br><span style="padding-right: 0.1px"><span class="cm-tag cm-bracket" style="color: #117700"></span><span class="cm-tag" style="color: #117700">body</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span><br><span style="padding-right: 0.1px"><span class="cm-tag cm-bracket" style="color: #117700"></span><span class="cm-tag" style="color: #117700">html</span><span class="cm-tag cm-bracket" style="color: #117700">></span></span></span></span></span></span></span></span></span></span>

运行结果如下

API

简单介绍下WebSocket的api

<span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">// WebSocket Api</span></span><br><span style="padding-right: 0.1px"><span class="cm-keyword" style="color: #770088">let</span> <span class="cm-def" style="color: #0000ff">socket</span> <span class="cm-operator" style="color: #981a1a">=</span> <span class="cm-keyword" style="color: #770088">new</span> <span class="cm-variable" style="color: #000000">WebSocket</span>(<span class="cm-variable" style="color: #000000">url</span>, [<span class="cm-variable" style="color: #000000">protocol</span>] ); <span class="cm-comment" style="color: #aa5500">// 实例化一个WebSocket对象建立连接</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">/**</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">* socket的readyState属性</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">* 0 - 表示连接尚未建立。</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">* 1 - 表示连接已建立，可以进行通信。</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">* 2 - 表示连接正在进行关闭。</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">* 3 - 表示连接已经关闭或者连接不能打开。</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">*/</span></span><br><span class="cm-tab-wrap-hack" style="padding-right: 0.1px"><span class="cm-variable" style="color: #000000">socket</span>.<span class="cm-property" style="color: #000000">readyState</span></span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">/**</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">* 只读属性 bufferedAmount 已被 send() 放入正在队列中等待传输，但是还没有发出的 UTF-8 文本字节数。</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">*/</span></span><br><span style="padding-right: 0.1px"><span class="cm-variable" style="color: #000000">socket</span>.<span class="cm-property" style="color: #000000">bufferedAmount</span></span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">/**</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">* WebSocket 事件</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">*/</span></span><br><span style="padding-right: 0.1px"><span class="cm-variable" style="color: #000000">socket</span>.<span class="cm-property" style="color: #000000">onopen</span>(); <span class="cm-comment" style="color: #aa5500">//连接建立时触发</span></span><br><span style="padding-right: 0.1px"><span class="cm-variable" style="color: #000000">socket</span>.<span class="cm-property" style="color: #000000">onmessage</span>(); <span class="cm-comment" style="color: #aa5500">//客户端接收服务端数据时触发</span></span><br><span style="padding-right: 0.1px"><span class="cm-variable" style="color: #000000">socket</span>.<span class="cm-property" style="color: #000000">onerror</span>(); <span class="cm-comment" style="color: #aa5500">//通信发生错误时触发</span></span><br><span style="padding-right: 0.1px"><span class="cm-variable" style="color: #000000">socket</span>.<span class="cm-property" style="color: #000000">onclose</span>(); <span class="cm-comment" style="color: #aa5500">//连接关闭时触发</span></span><br><span style="padding-right: 0.1px"></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">/**</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">* WebSocket 方法</span></span><br><span style="padding-right: 0.1px"><span class="cm-comment" style="color: #aa5500">*/</span></span><br><span style="padding-right: 0.1px"><span class="cm-variable" style="color: #000000">Socket</span>.<span class="cm-property" style="color: #000000">send</span>() <span class="cm-comment" style="color: #aa5500">//使用连接发送数据</span></span><br><span style="padding-right: 0.1px"><span class="cm-variable" style="color: #000000">Socket</span>.<span class="cm-property" style="color: #000000">close</span>() <span class="cm-comment" style="color: #aa5500">//关闭连接</span></span><br><span style="padding-right: 0.1px"><br></span>