Question

105

Javascript - Using Promises on Websocket?

rated 0 times [ 106] [ 1] / answers: 1 / hits: 45047 / 7 Years ago, fri, february 17, 2017, 12:00:00

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.

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.

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');

    });

}

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kaia

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answered 7 Years ago joaquin · Accepted Answer

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.

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);

        };



    });

}

Then, you would use it like this:

connect().then(function(server) {

    // server is ready here

}).catch(function(err) {

    // error here

});

or with async/await like this:

async myMethod() {

  try {

      let server = await connect()

      // ... use server

  } catch (error) {

      console.log(ooops , error)

  }

}