How to overcome issue of ".. is not function" while referring to earlier defined function expression in same js file : On accessing function expression in same file, gives error of .. "is not a function". 
I need this below function expression to be available both outside the js file to other .js files and as well inside the same js file.



I have tried below things from below blogs,nothing seems working
https://github.com/nodejs/node/issues/2923

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_function



    // this is in abc.js
    function qpValidations() {
         this.addDaystoGetDate = function(noOfDays){
         ... 
         }
          
          this.constructDate = function(){
            this.addDaystoGetDate (2);// here issue is coming
          }
    
    }
    module.exports = new qpValidations();


    //need addDaystoGetDate () function to be called in another file as below
    var qpFns = require(abc.js);
    qpFns.addDaystoGetDate() working as expected.
    
    This is the exact error shown
    Failed: this.addDaystoGetDate is not a function

Any help is most appreciated!!, though this issue occured many times with me, tried avoiding file circular dependency and as well clubbing function expression and declaration, had solved the issues earlier, but now again it has poped up not sure what the root cause of this issue..?