cassidoo's interview question #1

dateOffset.js

// first solution "pretty"
const days = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday'];
const dateOffset = (_day, _offset) => {
  const day = days.indexOf(_day);
  const offset = _offset % 7;
  const sum = day + offset;
  if ((day + offset) > days.length) {
    return dateOffset(days[day], (day + offset) - days.length);
  } else {
    return days[day + offset];
  }
};

// first solution: uglyfied
const days = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday'];
const dateOffset = (day, offset) => ((days.indexOf(day) + offset % 7) > days.length)
  ? dateOffset(days[days.indexOf(day)], (days.indexOf(day) + (offset % 7)) - days.length)
  : days[days.indexOf(day) + (offset % 7)];

// first solution: oneline
const days = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']; const dateOffset = (day, offset) => ((days.indexOf(day) + Number(offset) % 7) > days.length) ? dateOffset(days[days.indexOf(day)], (days.indexOf(day) + (Number(offset) % 7)) - days.length) : days[days.indexOf(day) + (Number(offset) % 7)];

// second solution: "pretty"
let dateOffset = (day, offset = 0) =>
  (
    ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']
      .reduce(
        (x, y, z, days) =>
          (
            z + 1 === 7 && (
                (offset < 0)                                                 // if (input is negative)
                  ? (days.indexOf(day) + (offset % 7)) < 0                     // if (past array length on the left side)
                    ? days[7 - Math.abs((days.indexOf(day) + (offset % 7)))]     // true: 7 - abs(index + (-offset))
                    : days[days.indexOf(day) - (offset % 7)]                     // false: index - offset
                  : (days.indexOf(day) + (offset % 7)) >= 7                  // else if (past array length on the right side)
                    ? days[days.indexOf(day) + (offset % 7) - 7]               // true: index + offset - 7
                    : days[days.indexOf(day) + (offset % 7)]                   // false: index + offset
              )
          ),
          0,
      )
  )
*/

// second solution - oneline challenge accepted  ᕦ(ツ)ᕤ
// 437 characters total 
// 365 characters without spaces
// no usage of ';' only one expression in the entire line ;)
let dateOffset = (day, offset = 0) => ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday'].reduce((x, y, z, days) => z + 1 === 7 && offset < 0 ? (days.indexOf(day) + (offset % 7)) < 0 ? days[7 - Math.abs(days.indexOf(day) + (offset % 7))] : days[days.indexOf(day) - (offset % 7)] : (days.indexOf(day) + (offset % 7)) >= 7 ? days[days.indexOf(day) + (offset % 7) - 7] : days[days.indexOf(day) + (offset % 7)], 0)