Calculates the backward difference of an array.

backdifference.js

function factorial(x) {
  if(x ===0) return 1;
  return x === 1 || x ===0 ? x : x * factorial(x - 1) ;
}

function binomial (n, k) {
    if (!Number.isInteger(n) || !Number.isInteger(k)) {
      return false;
    }
    return factorial(n) / (factorial(k) * factorial(n-k));
}

function nThDifference(array, n){
  
    if (!Number.isInteger(n)) {
      return false;
    }
    // Check if inputs are OK
    var difference = 0;
    if(array.length < n+1){
        //Zero pad to add zeros
        for(var i=0;i<n+1-array.length;i++){
            array.unshift(0);
        }
    }
    for(var i=0;i<n+1;i++){
      console.log(array[array.length-1-i]);
        difference =  difference+ Math.pow(-1,i)*binomial(n,i)*array[array.length-i-1];
    }
    return difference;
}

var a = [5.0, 5.4, 	6.0, 6.8, 7.5,8.1];

console.log(nThDifference(a,5))