Find the adjacent equal values in an arr of values

golSustains.js

// this function is rather long for doing something simple.
function getSustainedPeriods(arr) {
  let life = [];
  let lifeCount = 0;
  let death = [];
  let deathCount = 0;

  for (var i = 0; i < arr.length; i++) {
    if (arr[i] === 1) {
      life[lifeCount] === undefined ? life[lifeCount] = [1] : life[lifeCount] = [...life[lifeCount], 1];
    } else lifeCount += 1;

    if (arr[i] === 0 ) {
      death[deathCount] === undefined ? death[deathCount] = [1] : death[deathCount] = [...death[deathCount], 1];
    } else deathCount += 1;
  }

  // remove empty values
  life = life.filter(n => true)
             .map(subArr => {
               return subArr.reduce((a, b) => a + b);
             });

  death = death.filter(n => true)
               .map(subArr => {
                 return subArr.reduce((a, b) => a + b);
               });

  return { life, death };
}