blog-double-callback-invocation.js

function asyncFunction(cb) {
  process.nextTick(function () {
    try {
      var json = JSON.parse('{}');
      cb(null, json);
    } catch (e) {
      cb(e);
    }
  });
}

asyncFunction(function (err) {
  console.log(arguments);
  throw new Error('should never happen, right?');
});

/* console output

/U/n/tmp$ node asynctrycatch.js
{ '0': null, '1': {} }
{ '0': [Error: should never happen, right?] }

/Users/nicholascloud/tmp/asynctrycatch.js:14
  throw new Error('should never happen, right?');
        ^
Error: should never happen, right?
    at /Users/nicholascloud/tmp/asynctrycatch.js:14:9
    at /Users/nicholascloud/tmp/asynctrycatch.js:7:7
    at process._tickCallback (node.js:419:13)
    at Function.Module.runMain (module.js:499:11)
    at startup (node.js:119:16)
    at node.js:906:3
*/