hasDuplicates

Checks if there are duplicate values in a flat array.

• Use Set() to get the unique values in the array.
• Use Set.prototype.size and Array.prototype.length to check if the count of the unique values is the same as elements in the original array.

const hasDuplicates = arr => new Set(arr).size !== arr.length;

hasDuplicates([0, 1, 1, 2]); // true
hasDuplicates([0, 1, 2, 3]); // false