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javascript - 无法从 websocket 消息对象获取 json 值

问题描述

我想从 websocket 连接接收消息并将它们显示为推送通知，如下所示：

socket.onmessage = msg => {
  if( 'Notification' in window){
    if (Notification.permission === 'granted') {
        navigator.serviceWorker.ready.then(function(registration) {
        doNotify(msg);
        });
    }
    else{
        Notification.requestPermission()
            .then(function(result) {
                console.log(result);  //granted || denied
                if( Notification.permission == 'granted'){ 
                    doNotify();
                }
            })
            .catch( (err) => {
                console.log(err);
            });
    }

}
};

function doNotify(msg) {
  console.log('msg to deal with  is:', msg) ;
  console.log('type of message: ', typeof msg);
  let msgJ = JSON.stringify(msg);
  console.log('msg in json format:', msgJ) ;
  console.log('type of msgJ: ', typeof msgJ);
  console.log('sender:', msgJ.data.sender) ;
  console.log(' body:', msgJ.data.body) ;

  let title = "Message from" +  msgJ.data.sender;
  let body = msgJ.data.body;
  let options = {
    title:  title,
    body:   body,
    vibrate: [100, 200, 100]
  }
  let n = new Notification(title, options);

}

但是，我似乎无法从收到的消息中提取title和提取。body

以下是控制台日志结果：

msg to deal with  is: MessageEvent {isTrusted: true, data: "{"sender":"tomtom","body":"Hi there"}↵", origin: "ws://127.0.0.1:8080", lastEventId: "", source: null, …}
type of message:  object
msg in json format: {"isTrusted":true}
type of msgJ:  string
socket.js?1579263492:52 Uncaught (in promise) TypeError: Cannot read property 'sender' of undefined
    at doNotify (socket.js?1579263492:52)
    at socket.js?1579263492:17

这里有什么问题？我该如何解决？

标签： javascriptjsonwebsocket

解决方案

MessageEvent.data正如@chg 已经指出的那样，看起来像 JSON 字符串，因此您需要将其转换为对象。

let data = JSON.parse(msg.data);
let title = "Message from " +  data.sender;

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