Calling an asynchronous javascript function on server

Question

Can anyone please advise:

I have written a client side webpage which has a Websocket connection to a server side node app. All works fine.

When a certain message is sent through the websocket form the client I get the server to respond (again through the Websocket connection) with some text and I display that on the client side when the reposnse is received. All works fine.

Now, what if I want to make the function on the server an asynchronous one, which waits 4 seconds before returning the string. I can't get that to work, the string is returning as "[object Promise]".

So, the original synchronous code on the server,which is executed in reposnse to the client calling and is working is:

Chatterer.prototype.HandleASCIIMessage = function(szMessage, ws)
{
    ws.send("BANG");
}

Now I have replaced this by with:

Chatterer.prototype.HandleASCIIMessage = function (szMessage, ws)
{
    var sz = this.Test();
    ws.send(sz);
}

Where Test is:

Chatterer.prototype.Test = function()
{
    return this.ShowResult();
}

And the remainder of the code is:

Chatterer.prototype.ShowResult = async function ()
{
    var result = await this.GetAsync();

    return result;
}

Chatterer.prototype.GetAsync = async function ()
{
    var result = await this.AsyncFunc();

    return result;
}

Chatterer.prototype.AsyncFunc = async function ()
{
    return new Promise(resolve => {
        setTimeout(() => {
            resolve("BANG");
        }, 4000);
    });
}

I am trying to not have the ws.send(sz) line called until the 4 seconds is up.

Thanks, Mitch.

Answer 1

Chatterer.prototype.ShowResult = async function ()
{
    var result = await this.GetAsync();

    return result;
}

The above function returns a promise (an async function returns a promise). This means that the following returns a promise too:

Chatterer.prototype.Test = function()
{
    return this.ShowResult();
}

You could make the above async as well to make it more obvious, yet it's not technically needed.

This means that here:

Chatterer.prototype.HandleASCIIMessage = function (szMessage, ws)
{
    var sz = this.Test();
    ws.send(sz);
}

sz is a promise, so either make HandleASCIIMessage async and var sz = await this.Test();, or use the vanilla Promise API with this.Test().then(sz => ws.send(sz)).