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

id, title, isRequired, challengeType

id	title	isRequired	challengeType
af7588ade1100bde429baf20	Missing letters	true	5

Description

Find the missing letter in the passed letter range and return it. If all letters are present in the range, return undefined. Remember to use Read-Search-Ask if you get stuck. Try to pair program. Write your own code.

Instructions

Tests

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

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;
}