PrinterErrors.js

/**
 * Description:
 * In a factory a printer prints labels for boxes. For one kind
 * of boxes the printer has to use colors which, for
 * the sake of simplicity, are named with letters from a to m.
 *
 * The colors used by the printer are recorded in a control string.
 * For example a "good" control string would be aaabbbbhaijjjm
 * meaning that the printer used three times color a, four times color b,
 * one time color h then one time color a...
 *
 * Sometimes there are problems: lack of colors, technical malfunction
 * and a "bad" control string is produced e.g. aaaxbbbbyyhwawiwjjjwwm
 * with letters not from a to m.
 *
 * You have to write a function printer_error
 * which given a string will return the error rate of the
 * printer as a string representing a rational
 * whose numerator is the number of errors and the denominator
 * the length of the control string. Don't reduce this fraction
 * to a simpler expression.
 *
 * The string has a length greater or equal to one and contains
 * only letters from ato z.
 *
 *
 * Examples:
 *
 * s="aaabbbbhaijjjm"
 * printer_error(s) => "0/14"
 * s="aaaxbbbbyyhwawiwjjjwwm"
 * printer_error(s) => "8/22"
 *
 * Kata URL: https://www.codewars.com/kata/56541980fa08ab47a0000040/javascript
 *
 * @param {*} s
 * @returns
 */

function printerError(s) {
  let countError = 0;
  Array.from(s).forEach((char) => {
    /[a-mA-M]/gm.test(char) ? countError : countError++;
  });
  return countError + "/" + s.length;
}