pipeline.js

const apples = ['green', 'red', 'red', 'yellow', 'red', 'yellow', 'green', 'green'];

var appleMap = apples.reduce((prev, apple) => {
  if (prev[apple] >= 1) prev[apple]++;
  else prev[apple] = 1;
  return prev;
}, {});

console.log(appleMap);
// result: {green: 3, red: 3, yellow: 2}