Get the number of occurrences of every item in an array

uniqueValuesArray.js

// sample -> [ 1, 2, 1, 'a', [ 'd', 5, 6 ], 'A', 2, 'b', 1, 'd' ];
// result -> { 1: 3, 2: 2, a: 1...}

function flattenArray (arr, result) {
  result = result || [];
  
  for (var i = 0; i < arr.length; i++) {
    if (Array.isArray(arr[i])) {
      flattenArray(arr[i], result);
    } else {
      result.push(arr[i]);
    }
  }
  
  return result;
};

var uniqueValues = flattenArray(arr).reduce(function (prev, cur) {
  if (Object.keys(prev[cur]) === undefined) {
    prev[cur] = 1;
  } else {
    prev[cur] += 1;
  }

  return prev;
}, {});