How to get data from AngularJS callback function in loopback?

You need to return the promise, currently you are returning the array before it is updated. Async works by running all the synchronous code first then running anything async.

var arr = []; // runs first
promise.then(function(result){arr = result}) // runs third.
return arr; // runs second 

You need to change your code to return the promise. However this also means your calling code has to handle async code.

function asyncFunc() {
 return promise.then(function(result){return result});
}

asyncFunc().then(function(result) {console.log(result)}) // output is the value of result.

In the context of the code you gave above

app.run(function($rootScope,Communications,$http,$filter) {

$rootScope.getCommunication = 
function(object_type,val,id,isType,isSendSms,getNotes){
  // getting data from mysql data 
  return Communications.find({
        filter: {
          where: {
            and : [{
              communications_type_code : val
            },{
              object_id : id
            },{
              object_type : object_type
            }]
          }
        } 
      }).$promise
        .then(function(data) {
          var array = {};
          var newArray = [];
          for(var ind=0; ind<data.length; ind++){
            array['address_type'] = data[ind].address_type;
            array['contact_value'] = data[ind].contact_value;
            array['send_sms'] = data[ind].send_sms;
          }

          newArr.push(array);
           return newArr;
        });
};
});

and the calling function:

var arr = $rootScope.getCommunication(2,3,$id)
                    .then(function(arr){console.log(arr)})

You can use callback in following way

app.run(function($rootScope,Communications,$http,$filter) {

$rootScope.getCommunication = 
function(object_type,val,id,isType,isSendSms,getNotes, callback){

  var array = {};
  var newArr = [];

  // getting data from mysql data 
  var myVals = Communications.find({
        filter: {
          where: {
            and : [{
              communications_type_code : val
            },{
              object_id : id
            },{
              object_type : object_type
            }]
          }
        } 
      }).$promise
        .then(function(data) {

          for(var ind=0; ind<data.length; ind++){
            array['address_type'] = data[ind].address_type;
            array['contact_value'] = data[ind].contact_value;
            array['send_sms'] = data[ind].send_sms;
          }

          newArr.push(array);

           //return using callback
           return callback(newArr);

        });

  //return using callback
  return callback(newArr);

};
});

And use callback to access result

$rootScope.getCommunication(2,3,$id, function(result){
  var arr = result
})