async calls

[dvv]

Hi!

How do I manage a client to call a server-side async function (the one that doesn't return the result but instead calls a given callback)?

TIA,
--Vladimir

[ericz]

Hi Vladimir,

Server side async functions are 100% supported.

Simply pass in a callback.The tricky part is you must also pass in a 2nd callback for the return value.

Here is an example

Server:

var everyone = require("now").initialize(httpServer);

everyone.now.getServerInfo = function(callback){
  doAsync(function(data){
    callback(data);
  });
}

Client:

now.getServerInfo(function(data){
  // this is the callback of the async function
}, function(returnVal){
  // this contains the return value, which will be undefined since the server function doesn't      return anything.
});

[dvv]

Very well. Thanks!

[scottburch]

I tried this and it does not seem to work.

[dvv]

It does work for me.

server:

everyone.now.getServerInfo = function(arg, callback){
  callback('Hello from ' + arg);
}

client:

now.getServerInfo('async function', function(result){
  console.log(result); // 'Hello from async function'
},function(){});

Notice the noop second parameter

[ericz]

Hi guys,

In yesterday's release (v0.3) we have decided to eliminate the necessity of the noop second parameter that dvv has shown. This is because return values are no longer supported. Instead async callbacks should be used.

Considering server code:

 everyone.now.getServerInfo = function(callback){
   callback('Hello');
   return "Bye";
 }

And client code:

In v0.2 you could do this (this is no longer valid in the latest release):

 now.getServerInfo(function(data){
   // data contains 'Hello'
 }, function(returnVal){
   // this contains 'Bye'
 });

But v0.3 this must be changed to

 now.getServerInfo(function(data){
   // data contains 'Hello'
 });

As you can see this gets rid of the confusing noop callback that you would have to use in v0.2. Originally that was used for return values from the server function, but we found people rarely used return values so we decided to eliminate the confusing element in v0.3

[dvv]

Very well.

[dvv]

0.3: now.getServerInfo(console.log) throws 'Illegal invocation'. So one can not use natives as callback?

[ericz]

@dvv, yes this is a known issue. It's not possible to do nativeFunction.apply(...) as that throws the illegal invocation

[dvv]

np