[freecodecamp] Reverse a String / Factorialize a Number / Check for Palindromes

Reverse a String

function reverseString(str) {
  return str.split('').reverse().join('');
}

reverseString("hello");

Factorialize a Number

For example: 5! = 1 * 2 * 3 * 4 * 5 = 120

// 내가 푼 것
function factorialize(num) {
  var result = 1;
  for (var i = 2; i <= num; i++) {
    result = result * i;
  }
  return result;
}

factorialize(5);

// 다른 풀이
function factorialize(num) {
  return (num === 0) ? 1 : num * factorialize(num - 1);
}

factorialize(5);

Check for Palindromes

앞, 뒤로 똑같은 영어 단어 ~
특수문자, 공백 무시

You’ll need to remove all non-alphanumeric characters (punctuation, spaces and symbols) and turn everything lower case in order to check for palindromes.
We’ll pass strings with varying formats, such as "racecar", "RaceCar", and "race CAR" among others.
We’ll also pass strings with special symbols, such as "2A3*3a2", "2A3 3a2", and "2_A3*3#A2".

// 내가 푼 것
function palindrome(str) {
  var forwardStr = str.toLowerCase().replace(/[\W_]/g, '');
  var reverseStr = forwardStr.split('').reverse().join('');
  return forwardStr === reverseStr;
}

palindrome("eye");

// 다른 풀이
function palindrome(str) {
  str = str.toLowerCase().replace(/[\W_]/g, '');

  for (var i = 0, len = str.length - 1; i < (len/2); i++) {
    if (str[i] !== str[len - i]) { return false; }
  }
  return true;
}

/[\W_]/g

/ ... /g It’s a global regex. So it’ll operate on multiple matches in the string.
[ ... ] This creates a character set. Basically it’ll match any single character within the listed set of characters.
\W_ This matches the inverse of “word characters” and underscores. Any non-word character.

Then you have a few one off replacements for comma and period. Honestly, if that’s the complete code, /[\W_,.]/g, omitting the two other replaces, would work just as well.