Calculate the ranking of a JavaScript array

The ranking of an array is a list of the positions of its elements, based on a comparator function. This can be useful for sorting algorithms or ranking items in a list for display purposes.

In order to implement this, you can use Array.prototype.map() to iterate over each element and map it to its ranking. In order to calculate the ranking, you can use Array.prototype.filter() to count the number of elements that are smaller than the current element, based on the provided comparator function, compFn.

const ranking = (arr, compFn) =>
  arr.map(a => arr.filter(b => compFn(a, b)).length + 1);

ranking([8, 6, 9, 5], (a, b) => a < b);
// [2, 3, 1, 4]
ranking(['c', 'a', 'b', 'd'], (a, b) => a.localeCompare(b) > 0);
// [3, 1, 2, 4]