filterNonUnique
Filters out the non-unique values in an array.
Use Array.prototype.filter()
for an array containing only the unique values.
typescript
const filterNonUnique = (arr) =>
arr.filter((i) => arr.indexOf(i) === arr.lastIndexOf(i));
typescript
filterNonUnique([1, 2, 2, 3, 4, 4, 5]); // [1, 3, 5]