Yosemite Decimal System validator & comparator

yds-utils.js

// match 5.0 up to 5.15 including + and -. Example: 5.10+ or 5.12-
const REGEX_5_X = RegExp(/^5\.([0-9]|1[0-5])([+-]?)$/);

// match 5.10x to 5.15x. Example: 5.12c
const REGEX_5_10_LETTER = RegExp(/^5\.(1[0-5])([abcd])(?:\/[abcd])?$/);

/**
 * Test if a grade string is in valid format
 * @param {yds} grade
 */
export const is_valid = (grade) => get_weight(grade) !== -99;

export const get_weight = (grade) => {
  if (grade === "3rd") return -3;
  if (grade === "4th") return -2;
  if (grade === "Easy 5th") return -1;

  const m1 = REGEX_5_X.exec(grade);
  const m2 = REGEX_5_10_LETTER.exec(grade);

  if (m1 && m1.length > 1) {
    // 5.10- ==> 5.10a
    // 5.10+ ==> 5.10c
    // 5.10 ==> 5.10c
    const bias = m1[2] === "-" ? 1 : 3;
    return Number(m1[1]) * 10 + bias;
  } else if (m2 && m2.length > 1) {
    const letter = m2.length > 2 ? m2[2].charCodeAt(0) - 96 : 0;
    return Number(m2[1]) * 10 + letter;
  }

  return -99;
};

/**
 * YDS comparator.  Letter grade convention:  
 * 5.10- == 5.10a
 * 5.10 == 5.10c
 * 5.10c < 5.10d
 * 5.10d < 5.11-
 *
 * @param a
 * @param b
 */
export const comparator = (a, b) => {
  const w_a = get_weight(a);
  const w_b = get_weight(b);
  if (w_a < w_b) return -1;
  if (w_a > w_b) return 1;
  return 0;
};

Live codesandbox

How to sort a list

import { comparator } from "./yds-utils.js"

unsorted = ["5.11-",  "5.10d", "5.10" ,"5.10a", "5.8", "5.9+", "5.15"]

console.log(unsorted.sort(comparator))

Result ==>

5.8

5.9+

5.10a

5.10

5.10d

5.11-

5.15