title: filterNonUnique tags: array,beginner

Filters out the non-unique values in an array.

Use Array.prototype.filter() for an array containing only the unique values.

const filterNonUnique = (arr) =>
  arr.filter((i) => arr.indexOf(i) === arr.lastIndexOf(i));

filterNonUnique([1, 2, 2, 3, 4, 4, 5]); // [1, 3, 5]