Flexible Years

years.js

const data = [
  { fyStart: 'FY18', fyEnd: 'FY18' },
  { fyStart: 'FY18', fyEnd: 'FY20' },
  { fyStart: 'FY17', fyEnd: 'FY18' }
];

const start = data.map(d => d.fyStart.replace('FY', '')).sort();
const end = data.map(d => d.fyEnd.replace('FY', '')).sort();
const uniqueYears = Array.from(new Set([...start, ...end]));

let firstYear = uniqueYears[0] - 1; // this adds a year before the first year
let lastYear = uniqueYears[uniqueYears.length - 1];
let totalYears = 6; // we will show 6 years in the dyanmic data
var missingYears = [];

// data will come back with holes in the numbers, such as [18, 20]. Need to fill in missing years
for (let i = firstYear; i <= uniqueYears[uniqueYears.length - 1]; i++) {
    if (uniqueYears.indexOf(i) === -1) {
        missingYears.push(i);
    }
}

// need to always have it at a minimum of 6 years, so we have to check that the array has 6 items
let fillExtraYears = totalYears - missingYears.length;
if (fillExtraYears > 0) {
  for (let i = 1; i <= fillExtraYears; i++) {
    missingYears.push(Number(lastYear) + i);
  }
} else {
  // oh no, way too many years, you are getting capped to 8 years
  let extraYears = totalYears + 2;
  missingYears.splice(extraYears);
}

console.log(missingYears); // [ 16, 17, 18, 19, 20, 21 ]

// if you change FY20 above to a higher number, such as FY23, you can test again and you will get
// [ 16, 17, 18, 19, 20, 21, 22, 23 ]
// this is the use case of where there could be more than 6 years so allow it to go to 8
// change to even higher number and see that it will always get set to no more than 8 years