Javascript - 在 Websocket 上使用承诺? [英] Javascript - Using Promises on Websocket?

问题描述

我在纯 Javascript 中使用 Websockets，我想在 Websocket 函数中实现 Promises.我没有收到任何错误，但 Promise 不起作用.

I am using Websockets in pure Javascript and I want to implement Promises into the Websocket functions. I don't get any errors but the Promise doesn't work.

使用以下代码，我可以成功连接到 socketserver，但 Promise 似乎被跳过，因为警报的输出总是失败".

Using the following code I can connect succesful to the socketserver but the Promise seems to be skipped because the output of the alert is always "failed".

有人知道这种情况下的问题是什么吗?Ps:我在最新的 Google Chrome 浏览器和最新的 Mozilla Firefox 浏览器中进行了测试，在这个例子中我省略了一些基本的检查/错误处理.

Does somebody knows what the problem is in this case? Ps: I did the tests in the latest Google Chrome browser and the latest Mozilla Firefox browser, and I left out some basic checking/error handling for this example.

function Connect()
{
    server = new WebSocket('mysite:1234');

    server.onopen = (function()
    {
        return new Promise(function(resolve, reject) 
        {
            if (true)
            {
                resolve();
            }
            else
            {
                reject();
            }
        });
    }).then = (function()
    {
        alert('succeeed');
    }).catch = (function()
    {
        alert('failed');
    });
}

推荐答案

您尝试在新连接中使用 Promise 似乎有点误导.您将希望从 connect() 返回一个承诺，以便您可以使用它来知道服务器何时连接.

Your attempt to use promises with the new connection seems a bit misguided. You will want to return a promise from connect() so you can use it to know when the server is connected.

看起来你可能想要这样的东西:

It seems like you probably want something like this:

function connect() {
    return new Promise(function(resolve, reject) {
        var server = new WebSocket('ws://mysite:1234');
        server.onopen = function() {
            resolve(server);
        };
        server.onerror = function(err) {
            reject(err);
        };

    });
}

然后，您可以像这样使用它:

Then, you would use it like this:

connect().then(function(server) {
    // server is ready here
}).catch(function(err) {
    // error here
});

或者像这样async/await:

async myMethod() {
  try {
      let server = await connect()
      // ... use server
  } catch (error) {
      console.log("ooops ", error)
  }
}

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