Checks if all elements in an array are unique, based on the provided mapping function.

  • Use to apply fn to all elements in arr.
  • Create a new Set from the mapped values to keep only unique occurrences.
  • Use Array.prototype.length and Set.prototype.size to compare the length of the unique mapped values to the original array.
const allUniqueBy = (arr, fn) => arr.length === new Set(;
allUniqueBy([1.2, 2.4, 2.9], Math.round); // true
allUniqueBy([1.2, 2.3, 2.4], Math.round); // false