Add an approach to Poetry Club Door Policy

exercises/concept/poetry-club-door-policy/.approaches/config.json

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+{
+  "introduction": {
+    "authors": [
+      "Yrahcaz7"
+    ]
+  }
+}

exercises/concept/poetry-club-door-policy/.approaches/introduction.md

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+# Introduction
+
+There are various ways to solve each part of Poetry Club Door Policy.
+A commonality between most of the parts is needing to get a character from the provided string.
+
+There are multiple ways to do this, one of which is the standard way of using `[index]` access.
+
+One other way is to use [`charAt`][mdn-char-at], which is the same as `[index]` access for most purposes.
+
+Another method is [`at`][mdn-at], which is the same as `[index]` access, except it accepts negative numbers.
+A negative number will count backwards from the end of the string, unlike positive numbers, which count forwards from the start.
+
+In addition, [`substring`][mdn-substring] and [`slice`][mdn-slice] can be used.
+These string methods are normally used to get portions of strings, rather than a single character.
+
+An important distiction is that `slice` accepts negative numbers like `at` does, but `substring` does not.
+
+## Different ways to implement `frontDoorPassword`
+
+For `frontDoorPassword`, there are a variety of ways to make strings uppercase and lowercase.
+
+### Approach: `toUpperCase` and `toLowerCase`
+
+```js
+export function frontDoorPassword(word) {
+  return word[0].toUpperCase() + word.slice(1).toLowerCase();
+}
+```
+
+This approach is a standard method that uses [`toUpperCase`][mdn-to-upper-case] and [`toLowerCase`][mdn-to-lower-case].
+
+### Approach: `toLocaleUpperCase` and `toLocaleLowerCase`
+
+```js
+export function frontDoorPassword(word) {
+  return word[0].toLocaleUpperCase() + word.substring(1).toLocaleLowerCase();
+}
+```
+
+This approach uses [`toLocaleUpperCase`][mdn-to-locale-upper-case] and [`toLocaleLowerCase`][mdn-to-locale-lower-case], which are very similar to `toUpperCase` and `toLowerCase`, but work with either the current locale or a given locale, which can be specified as an argument.
+This approach is necessary when the language locale has a non-standard mapping between lower and uppercase.
+
+```javascript
+const str = 'istanbul';
+
+str.toUpperCase();
+// => 'ISTANBUL'
+str.toLocaleUpperCase('en-US');
+// => 'ISTANBUL'
+
+str.toLocaleUpperCase('tr');
+// => 'İSTANBUL'
+```
+
+### Approach: `String.fromCharCode` and `charCodeAt`
+
+```js
+export function frontDoorPassword(word) {
+  let charCode = word.charCodeAt(0);
+  if (charCode >= 97) {
+    charCode -= 32;
+  }
+
+  let password = String.fromCharCode(charCode);
+
+  for (let index = 1; index < word.length; index++) {
+    charCode = word.charCodeAt(index);
+    if (charCode <= 90) {
+      charCode += 32;
+    }
+
+    password += String.fromCharCode(charCode);
+  }
+  return password;
+}
+```
+
+This approach uses [`String.fromCharCode`][mdn-from-char-code] along with [`charCodeAt`][mdn-char-code-at].
+
+This method is much longer than the others and it only works with english letters, so it is less than ideal.
+
+## Different ways to implement `backDoorResponse`
+
+There are many ways to go about trimming whitespace for `backDoorResponse`.
+
+### Approach: `trim` and `[index]` access
+
+```js
+export function backDoorResponse(line) {
+  const trimmed = line.trim();
+  return trimmed[trimmed.length - 1];
+}
+```
+
+This standard approach uses `[index]` access and the built-in string method [`trim`][mdn-trim], which trims any leading and trailing whitespace from a string.
+
+### Approach: `trimEnd` and `at`
+
+```js
+export function backDoorResponse(line) {
+  return line.trimEnd().at(-1);
+}
+```
+
+This approach uses the string method [`trimEnd`][mdn-trim-end], which only trims trailing whitespace, unlike `trim`.
+
+It also uses `at` instead of `[index]` access make the solution shorter.
+
+### Approach: `replaceAll` and `charAt`
+
+```js
+export function backDoorResponse(line) {
+  const trimmed = line.replaceAll(' ', '');
+  return trimmed.charAt(trimmed.length - 1);
+}
+```
+
+This approach uses [`replaceAll`][mdn-replace-all] to remove all of the spaces in the string.
+
+This merges all the words in the string together, but that doesn't matter here as we only care about the last character and not the rest of the string.
+
+### Approach: `replace` and literal `RegExp`
+
+```js
+export function backDoorResponse(line) {
+  const trimmed = line.replace(/\s/g, '');
+  return trimmed[trimmed.length - 1];
+}
+```
+
+This approach uses [`replace`][mdn-replace] with a [regular expression literal][mdn-regular-expressions], achieving a similar result to the previous approach.
+
+The main difference is that the previous approach only removes spaces, while this approach can remove any type of whitespace.
+
+### Approach: `for` loop
+
+```js
+export function backDoorResponse(line) {
+  for (let index = line.length - 1; index >= 0; index--) {
+    if (line[index] != ' ') {
+      return line[index];
+    }
+  }
+  return '';
+}
+```
+
+This approach does not trim whitespace.
+Instead, it uses a [for loop][mdn-for] to return the first character that is not a space from the end of the string.
+
+[mdn-char-at]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/charAt
+[mdn-at]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/at
+[mdn-substring]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substring
+[mdn-slice]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice
+[mdn-to-upper-case]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toUpperCase
+[mdn-to-lower-case]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toLowerCase
+[mdn-to-locale-upper-case]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toLocaleUpperCase
+[mdn-to-locale-lower-case]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toLocaleLowerCase
+[mdn-from-char-code]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/fromCharCode
+[mdn-char-code-at]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/charCodeAt
+[mdn-trim]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim
+[mdn-trim-end]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trimEnd
+[mdn-replace-all]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replaceAll
+[mdn-replace]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace
+[mdn-regular-expressions]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_expressions
+[mdn-for]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for