Async with loop function task list node js

Question

Hello i am using async parallel in my code for practice code

var tasklist = [],tempjson={};
for(var i = 0; i < 10; i++)  {
   tempjson.data = 'i is' + i;
   for(var j = 0; j < 20; j++){
      tasklist.push(doSomething(tempjson,j));
   }
}
 async.parallel(taskList, function(err, data) {
       console.log(data);
 });

function doSomething(params,j){
       params.data2 = 'j value is'+ j
       return callback(null,params)
}

want to do something like that but i am getting error that callback is undefined can somebody help me what is wrong with code

Devang Naghera · Accepted Answer · 2018-04-03 06:31:23Z

1

You are not passing callback as a argument to the function doSomething.

Just add the callback argument like

function doSomething(params,j){
     return function(callback){
       params.data2 = 'j value is'+ j
       return callback(null,params)
     }   

}

This will solve the problem!!

edited Apr 3, 2018 at 6:31

answered Apr 3, 2018 at 6:26

Devang Naghera

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3 Comments

Dexter Over a year ago

getting error stack: 'TypeError: callback is not a function\n

Devang Naghera Over a year ago

Updated the answer!!, Sorry my bad

Dexter Over a year ago

thax bro for help

Sridhar · Accepted Answer · 2018-04-03 06:38:48Z

ReferenceError: callback is not defined

This is because you're not passing callback to doSomething(). As per docs, We need to pass callback to the function.

Also, there is a typo in your code. It is tasklist and not taskList

Fixing this,

  var tasklist = [], tempjson = {};
  for (var i = 0; i < 10; i++) {
    tempjson.data = 'i is' + i;
    for (var j = 0; j < 20; j++) {
      tasklist.push(function (callback) {
        doSomething(tempjson, j, callback);
      }); // Array of task as per docs
    }
  }
  async.parallel(tasklist, function (err, data) {
    console.log(data);
  });

  function doSomething(params, j, callback) { // passing callback as per docs
    params.data2 = 'j value is' + j;
    return callback(null, params)
  }

This will log

[ { data: 'i is9', data2: 'j value is20' },
{ data: 'i is9', data2: 'j value is20' },
... ... 100 more items ]

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