Question

I am not sure what the callback function should look like if I want to do this. Both functions are in a class and I really want to abstract it.

doesexist: function(setvalue) {
  redisclient.sismember('setname', setvaue, callbackfuntion(value));
}

someothermethod: function() {
  if (doesexist()){
    // doSomething
  }
}

How would I do that in an async environment?

UPDATE:

I now tried it that way (coffeescript):

deoesexist: (setvalue, cb) ->
  @r.sismember 'setname', setvalue, (err, res) -> cb(res)

someothermethod: (setvalue) ->
  @doesexist setvalue, (exists) =>
    unless exists
      # emit an event that calls a function
      # that probably adds the not existing value.
      # I just don't want to redo this. That's
      # what this function is all about

It seems to work pretty well like that.

Answer 1

You should checkout out control flow libraries, https://npmjs.org/browse/keyword/flow, to determine which approach is best for you, I prefer the async library https://github.com/caolan/async

To answer your question you would work your problem in the following way;

doesexist: function(setvalue, callback) {
    redisclient.sismember('setname', setvaue, callback);
}

someothermethod: function(somevalue) {
   doesexist(somevalue, function(err, exists) {
         if (exists) {
            // doSomething
         }
   })
}

I hope that helps!

Jay