How to get callback function value in node.js

Question

How to get callback function value in node.js

This is my Logic in one of my controller method

exports.index = function(req, res) {

   var empRole;
   EmpModel.findById(empId, null ,function(err, emp) {

      if(emp) {
         empRole = emp.role;          
      }
   });

   console.log("Emp Role : " + empRole);      // This will return undefined
};

How can I get the value of empRole from the call back function

node.js
mongoose

Answer 1

You can pass a callback to the index function and inside the "IF" condition use the callback to pass the value to the caller.

Example:

exports.index = function(callback) {

   var empRole;
   EmpModel.findById(empId, null ,function(err, emp) {

      if(emp) {
         empRole = emp.role;
         callback(empRole)
      }
   });


};

You need to invoke the index function like this:

index(function(emprole){
      //this function is executed once the findById completes
      console.log("Emp Role : " + empRole); 
});

Look into Callback's in javascript along with Closure to understand this better.