/*

  Functional Programming in JavaScript

  Author: Luis Atencio

  Referential Transparency 

*/

console.log('Referential Transparency');

​

var nums = [80, null, 90, 100];

var total = 0;

var validNums = 0;        

function calcAverage() {  

     // Depends on the external variable nums, 

     // total, validNums

     for(var i = 0; i < nums.length; i++) {                 

            if(nums[i] !== null || nums[i] !== undefined) {  

                total+= nums[i];

                validNums++;

            }

     }

     var newAverage = total / validNums;

     return Math.round(newAverage);

}

​

console.log('First call yields: ' + calcAverage());

​

// If the totalGrades variable changes in between calls, it compromises the 

// execution of average.

total = 100;

​

// Now, the call the same average call changes

console.log('Second call yields: ' + calcAverage());

​

/*

  EXERCISE: Make 'calcAverage' referentially transparent. Executing 'calcAverage' on the same input array should always yield the same result.

  */

​

function calcAverage2(/* provide calcAverage2 with 

  all necessary params */) {  

     // bring all variables into the scope of the function

     // calculate average

}

​

console.log(calcAverage2[80, 90, 100] === calcAverage2[80, 90, 100]);

​

​

​