Some node gotchas

a_module.js

exports.somethingAsync = function(callback) {
   setTimeout(function() {
     callback(null "done");
   }, 100);
}

exports.failingAsync = function(callback) {
   setTimeout(function() {
     callback(new Error("failed"));
   }, 100);
}

b_async_throw.js

var lib = require('a_module');

function getData(id, someParam, callback) {
  var data = {}

  lib.failingAsync(function(err, result) {
    // you should be returning here
    if(err) { return callback(err); }

    // no way to catch this because we're in a new stack
    if(!someParam) { throw new Error('Missing someParam'); }

    // do something with result
    data.result = result;

    // if there is was an error, this got called twice.
    callback(null, data));
  });
}

c_forgot_callback.js

var lib = require('a_module');


var myRegex = /some regex/;

function getData(callback) {
  var data = {}

  lib.somethingAsync(function(err, result) {
    // you should be returning here
    if(err) { return callback(err); }

    // do something non-trivial with result
    if(result.test(myRegex)) {
      data.result = result + " for getData";
      return callback(null, data);
    } else if(result == "stop now") {
      // don't continue
      return; // where's your callback in this case?
    } else {
      // return empty data
      return callback(null, data);
    }
  });
}

d_double_callback.js

var lib = require('a_module');


function getData(callback) {
  var data = {}

  lib.failingAsync(function(err, result) {
    // you should be returning here
    if(err) { callback(err); }

    // do something with result
    data.result = result;

    // if there is was an error, this got called twice.
    callback(null, data));
  });
}