descend.js

import _curry3 from './internal/_curry3';


/**
 * Makes a descending comparator function out of a function that returns a value
 * that can be compared with `<` and `>`.
 *
 * @func
 * @memberOf R
 * @since v0.23.0
 * @category Function
 * @sig Ord b => (a -> b) -> a -> a -> Number
 * @param {Function} fn A function of arity one that returns a value that can be compared
 * @param {*} a The first item to be compared.
 * @param {*} b The second item to be compared.
 * @return {Number} `-1` if fn(a) > fn(b), `1` if fn(b) > fn(a), otherwise `0`
 * @see R.ascend
 * @example
 *
 *      const byAge = R.descend(R.prop('age'));
 *      const people = [
 *        { name: 'Emma', age: 70 },
 *        { name: 'Peter', age: 78 },
 *        { name: 'Mikhail', age: 62 },
 *      ];
 *      const peopleByOldestFirst = R.sort(byAge, people);
 *        //=> [{ name: 'Peter', age: 78 }, { name: 'Emma', age: 70 }, { name: 'Mikhail', age: 62 }]
 */
var descend = _curry3(function descend(fn, a, b) {
  var aa = fn(a);
  var bb = fn(b);
  return aa > bb ? -1 : aa < bb ? 1 : 0;
});
export default descend;