string-theory.js

function onlyVowels(str) {
  let output = '';
  for (const char of str) {
    const lowerCaseChar = char.toLowerCase();
    if (
      lowerCaseChar === 'a' || 
      lowerCaseChar === 'e' || 
      lowerCaseChar === 'o' || 
      lowerCaseChar === 'u' || 
      lowerCaseChar === 'i'
    ) {
      output += char;
    }
  }
  return output;
}

function crazyCase(str) {
  let output = '';
  for (let i = 0; i < str.length; i++) {
    const char = str[i];

    // If index is even? Lower case the char
    if (i % 2 === 0) {
      output += char.toLowerCase();
    } 
    
    // Is the index odd? Upper case the char
    else {
      output += char.toUpperCase();
    }
  }
  return output;
}

function titleCase(str) {
  let output = '';
  let shouldCapitalizeNextLetter = true;
  for (const char of str) {
    
    // We should capitalize the char
    if (shouldCapitalizeNextLetter) {
      output += char.toUpperCase();
    }

    // We should lower case the char
    else {
      output += char.toLowerCase();
    }

    // Determine whether we should capitalize the next letter
    if (char === ' ') {
      shouldCapitalizeNextLetter = true;
    } else {
      shouldCapitalizeNextLetter = false;
    }

    // Simplification of above if statement:
    // shouldCapitalizeNextLetter = char === ' ';
  }

  return output;
}

function camelCase(str) {
  let output = '';
  let shouldCapitalizeNextLetter = false;
  for (const char of str) {

    // Add character to output string, unless its a space
    if (char !== ' ') {
      // If 'shouldCapitalizeNextLetter is true, capitalize
      // Otherwise, lowercase the char
      if (shouldCapitalizeNextLetter) {
        output += char.toUpperCase();
      } else {
        output += char.toLowerCase();
      }
    }

    // If the character is a space, capitalize the next letter
    // Otherwise, lower case the next letter
    if (char === ' ') {
      shouldCapitalizeNextLetter = true;
    } else {
      shouldCapitalizeNextLetter = false;
    }
  }
  return output;
}

function crazyCase2ReturnOfCrazyCase(str) {
  let output = '';
  let shouldCapitalizeNextLetter = false;
  for (const char of str) {

    // Add current char to output string, capitalize or lowercase as appropriate
    if (shouldCapitalizeNextLetter) {
      output += char.toUpperCase();
    } else {
      output += char.toLowerCase();
    }

    // Toggle `shouldCapitalizeNextLetter` if the current char is not a space
    if (char !== ' ') {
      shouldCapitalizeNextLetter = !shouldCapitalizeNextLetter;
    }
  }
  return output;
}