var votes = [
  'angular',
  'angular',
  'react',
  'react',
  'react',
  'angular',
  'ember',
  'react',
  'vanilla'
];

var initialValue = {};

var reducer = function(tally, vote) {
  if(!tally[vote]) {
    tally[vote] = 1;
  } else {
    tally[vote] = tally[vote] + 1;
  }

  return tally;
}

var result = votes.reduce(reducer, initialValue);

console.log(result);
// Object {angular: 3, react: 4, ember: 1, vanilla: 1}