What we need is closure - Basic

Basic Closure.js

var sodexoAmount = 25;
function getSalary(baseSalary) {
  var transportAmount = 50; 
  function calculateSalary(hraAmount) {
    var specialAllowance = 75;
    return specialAllowance + hraAmount + baseSalary + transportAmount + sodexoAmount; 
  }
  return calculateSalary;
} 
var monthlySalary = getSalary(100);
console.log(monthlySalary(125));