synchronous function call in node js

Question

I am trying to make synchronous call to functions in my node js code.

I am calling my functions like this

set_authentication();
set_file();

function  set_authentication(){
---
callback function
---
}

I want that my set_authentication() function should execute first completely and then set_file() should start execution but set_file() function start executing before the callback of set_authentication().

I have tried this using async also like

async.series(
        [
            // Here we need to call next so that async can execute the next function.
            // if an error (first parameter is not null) is passed to next, it will directly go to the final callback
            function (next) {
                set_looker_authentication_token();

            },
            // runs this only if taskFirst finished without an error
            function (next) {
                set_view_measure_file();
            }
        ],
        function(error, result){

        }
    );

but it also doesn't work.

I tried promise also

set_authentication().then(set_file(),console.error);

function  set_authentication(){
        ---
        callback function
        var myFirstPromise = new Promise((resolve, reject) => {

      setTimeout(function(){
        resolve("Success!");
      }, 250);
    }); 
       ---
        }

here I am getting this error:- Cannot read property 'then' of undefined.

I am new to node and js.

Answer 1

You need to return Promise, because you call .then method of a returned promise:

set_authentication().then(set_file);

function set_authentication() {
  return new Promise(resolve => {                 // <------ This is a thing
    setTimeout(function(){
     console.log('set_authentication() called');
     resolve("Success!");
    }, 250);
  });
}
        
function set_file(param) {
  console.log('set_file called');
  console.log(
    'received from set_authentication():', param);
}

Answer 2

If set_authentication is async func, you need to pass set_file as callback to set_authentication function.

You may also consider to use promises as you wrote, but you need to implement it before you start chaining.

Answer 3

use async.auto like this:

 async.auto(
                {
                    first: function (cb, results) {
                        var status=true;
                        cb(null, status)
                    },
                    second: ['first', function (results, cb) {
                        var status = results.first;
                        console.log("result of first function",status)
                    }],
                },
                function (err, allResult) {
                   console.log("result of executing all function",allResult)

                }
            );