freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/missing-letters.english.md

id, title, isRequired, challengeType, isHidden, forumTopicId

id	title	isRequired	challengeType	isHidden	forumTopicId
af7588ade1100bde429baf20	Missing letters	true	5	false	16023

Description

Find the missing letter in the passed letter range and return it. If all letters are present in the range, return undefined.

Instructions

Tests

tests:
  - text: <code>fearNotLetter("abce")</code> should return "d".
    testString: assert.deepEqual(fearNotLetter('abce'), 'd');
  - text: <code>fearNotLetter("abcdefghjklmno")</code> should return "i".
    testString: assert.deepEqual(fearNotLetter('abcdefghjklmno'), 'i');
  - text: <code>fearNotLetter("stvwx")</code> should return "u".
    testString: assert.deepEqual(fearNotLetter('stvwx'), 'u');
  - text: <code>fearNotLetter("bcdf")</code> should return "e".
    testString: assert.deepEqual(fearNotLetter('bcdf'), 'e');
  - text: <code>fearNotLetter("abcdefghijklmnopqrstuvwxyz")</code> should return undefined.
    testString: assert.isUndefined(fearNotLetter('abcdefghijklmnopqrstuvwxyz'));

Challenge Seed

function fearNotLetter(str) {
  return str;
}

fearNotLetter("abce");

Solution

function fearNotLetter (str) {
  for (var i = str.charCodeAt(0); i <= str.charCodeAt(str.length - 1); i++) {
    var letter = String.fromCharCode(i);
    if (str.indexOf(letter) === -1) {
      return letter;
    }
  }

  return undefined;
}