Hack to add .toSarcasm() method to javascript strings

toSarcasm.js

/*
 * A common way of denoting sarcasm in text on the internet is to alternate upper and lower casing in the text.
 * For example: "But I didn't do it!" might become "BuT i DiDn'T dO iT!"
 *
 * This adds a method to strings in JavaScript to convert them to this sarcastic format.
 *
 * The method returns a new string with the casing of each letter appropriately changed.
 * The method supports letters with diacritic marks, e.g., umlauts.
 *
 * By default, it will start the converted string in lowercase form
 *   e.g., "My feelings are hurt!".toSarcasm() -> "mY fEeLiNgS aRe HuRt!"
 *
 * Initial case can be preserved by passing in true:
 *   e.g., "My feelings are hurt!".toSarcasm(true) -> "My FeElInGs ArE hUrT!"
 */
Object.defineProperty(
  String.prototype,
  'toSarcasm',
  {
    value(preserveInitialCase = false) {
      const alphaRegex = /^[\p{Letter}\p{Mark}]$/u;
      let capitalize = false;
      let output = '';
      if (this.length) {
        if (preserveInitialCase) {
          capitalize = this[0] !== this[0].toLowerCase() && this[0] === this[0].toUpperCase();
        }
        for (const char of this) {
          if (alphaRegex.test(char)) {
            output += (capitalize ? char.toUpperCase() : char.toLowerCase());
            capitalize = !capitalize;
          } else {
            output += char;
          }
        }
      }
      return output;
    },
  },
);