Using promises when response callback

Question

I'm trying to figure out how to use promises in a test I'm writing. I'm using plain ol' native promises in the browser. No libraries (yet)

The test requires communicating asynchronously with a server, where I get the server response via a callback

I have a server object where I register the callback like so:

server.onresponse = function(data){
  //do stuff with data
}

The test requires sending a series of commands to the server that change based on the servers response. I send the commands to the server like so

server.sendCommand({data:"do something"})

Based on the command, the server would raise the onresponse callback. I would need to read the data that the server sent to decide what the next command should be.

The interaction should be something like

• send command 1 and wait
• process data from onresponse callback
• send command 2 and wait
• process data from onresponse callback

I would like to use promises to make this interaction read a bit clearer. Like something like a series of .then()s .

I realize promises cannot be reused so it's not like I can reset the same promise every time the onresponse callback happens.

Is there a way to do this via promises? I started reading out generators as well. Would those help too?

Thanks

Answer 1

You could have something like this:

function sendCommand(data) {
    return new Promise(function(resolve,reject) {
         server.onresponse = resolve;
         server.sendCommand(data);
    });
}

and use it like this:

sendCommand({data:"do something"})
.then(function(data) {
    console.log(data);
    return sendCommand({data:"do something else "})
})
.then(function(data) {
    console.log(data);
})