Node async.js: callback is not a function error?

Question

I have this code:

async = require('async')

async.auto({
   getUserName: function(callback) {
      console.log('**In getUserName.**')
      callback(null, 'Lem')
   },

   connectToDb: function(callback) {
      console.log('**In connectToDb.**')
      var connected = true
      if(connected) {
        callback(null, connected)
      } else {
        callback('Error connecting to DB.', null)
      }
   },

   checkIfUserExist: [
      'getUserName',
      'connectToDb',
      function(callback, results) {
         console.log('**In checkIfUserExist.**',          
            JSON.stringify(results))
         var userExist = false
         if(userExist) {
            callback('User exist in DB.')
         } else {
            setTimeout(
               function() {
                  callback(null, userExist);
               },
               1000
            );
         }
      }
   ],

   signup: [
      'checkIfUserExist',
      function(callback, results) {
         console.log('**In signup**', JSON.stringify(results))
         var userName = results.getUserName
         var isDbConnected = results.connectToDb
         var userExist = result.checkIfUserExist

        if(userName && isDbConnected && !userExist) {
           callback(null, 
             {'status': '200', 'msg': 'Successfully signed up user'})
       } else {
          callback('Error signing up user.', null)
       }
    }
  ]
 },
 function(error, results) {
    console.log('error = ', error)
    console.log('results = ', results)

})

Why am I experiencing this error:

**In getUserName.**
**In connectToDb.**
error =  function () {
    if (fn === null) throw new Error("Callback was already called.");
        var callFn = fn;
        fn = null;
    callFn.apply(this, arguments);
}
results =  undefined
**In checkIfUserExist.** undefined
^[[A/home/lem/js/async/asyncAuto.js:30
        callback(null, userExist);
        ^

TypeError: callback is not a function
   at Timeout._onTimeout (/home/lem/js/async/asyncAuto.js:30:13)
   at ontimeout (timers.js:365:14)
   at tryOnTimeout (timers.js:237:5)
   at Timer.listOnTimeout (timers.js:207:5)

in your instead of : signup: [ 'checkIfUserExist', function(callback, results) { use: signup: [ 'checkIfUserExist', function(err, results) { actually what node.js does is it first check the error in every function then it gives the result as a callback what you were doing is like you were passing callback as an error to which it gives you an error message — Shumi Gupta
– Shumi Gupta, Commented Oct 22, 2016 at 9:44

Sergey Lapin · Accepted Answer · 2016-10-22 08:34:06Z

4

There was a breaking change in async's auto method in v2, which you seem to use. https://github.com/caolan/async/blob/master/CHANGELOG.md#breaking-changes

auto task functions now always take the callback as the last argument. If a task has dependencies, the results object will be passed as the first argument. To migrate old task functions, wrap them with _.flip

answered Oct 22, 2016 at 8:34

Sergey Lapin

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Comments

Anish Agarwal · Accepted Answer · 2016-10-22 14:38:23Z

1

An async function, one that expects a callback as its last argument. Here is my working code.

    var async = require('async');
         async.auto({
           getUserName: function(callback) {
            console.log('**In getUserName.**')
            callback(null, 'Lem')
           },

         connectToDb: function(callback) {
          console.log('**In connectToDb.**')
          var connected = true
          if(connected) {
            callback(null, connected)
          } else {
            callback('Error connecting to DB.', null)
          }
       },
       checkIfUserExist: [
          'getUserName',
          'connectToDb',
          function(results, callback) {
             console.log('**In checkIfUserExist.**',          
                JSON.stringify(results))
             var userExist = false
             if(userExist) {
                callback('User exist in DB.')
             } else {               
                setTimeout(function() {                 
                      callback(null, userExist);
               },1000);
             }
          }
       ],

       signup: [
          'checkIfUserExist',
          function(results, callback) {
             console.log('**In signup**', JSON.stringify(results))
             var userName = results.getUserName
             var isDbConnected = results.connectToDb
             var userExist = results.checkIfUserExist

            if(userName && isDbConnected && !userExist) {
               callback(null, 
                 {'status': '200', 'msg': 'Successfully signed up user'})
           } else {
              callback('Error signing up user.', null)
           }
        }
     ],
},
     function(error, results) {
        console.log('error = ', error)
        console.log('results = ', results)         
    })

function(callback, results) should be function(results, callback)

Please check this url for reference. https://caolan.github.io/async/docs.html#auto

edited Oct 22, 2016 at 14:38

answered Oct 22, 2016 at 7:28

Anish Agarwal

1,81120 silver badges19 bronze badges

4 Comments

LEMUEL ADANE Over a year ago

Still has errors see next comment below. What does that mean?

LEMUEL ADANE Over a year ago

In getUserName. In connectToDb. error = function () { if (fn === null) throw new Error("Callback was already called."); var callFn = fn; fn = null; callFn.apply(this, arguments); } results = undefined In checkIfUserExist. {"getUserName":"Lem","connectToDb":true} In signup {"getUserName":"Lem","connectToDb":true,"checkIfUserExist":false}

LEMUEL ADANE Over a year ago

It turns out to be a mistake in the orientation of the curly braces.

Anish Agarwal Over a year ago

yes there was curly braces missed, I have update the code and now it's good.

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