freeCodeCamp/curriculum/challenges/chinese-traditional/02-javascript-algorithms-and-data-structures/functional-programming/refactor-global-variables-out-of-functions.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
587d7b8f367417b2b2512b60	在函數中重構全局變量	1	301235	refactor-global-variables-out-of-functions

--description--

目前爲止，我們已經看到了函數式編程的兩個原則：

1. 不要更改變量或對象 - 創建新變量和對象，並在需要時從函數返回它們。 提示：使用類似 var newArr = arrVar 時 arrVar 是一個數組，代碼只是創建一個對現有變量的引用，而不是副本。 所以更改 newArr 中的值會同時更改 arrVar 中的值。

2. 聲明函數參數 - 函數內的任何計算僅取決於參數，而不取決於任何全局對象或變量。

給數字增加 1 不夠刺激，我們可以在處理數組或更復雜的對象時應用這些原則。

--instructions--

重構代碼，使全局數組 bookList 在函數內部不會被改變。 add 函數可以將指定的 bookName 增加到數組末尾並返回一個新的數組（列表）。 remove 函數可以從數組中移除指定 bookName。

注意： 兩個函數都應該返回一個數組，任何新參數都應該在 bookName 參數之前添加。

--hints--

bookList 應等於 ["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"].

assert(
  JSON.stringify(bookList) ===
    JSON.stringify([
      'The Hound of the Baskervilles',
      'On The Electrodynamics of Moving Bodies',
      'Philosophiæ Naturalis Principia Mathematica',
      'Disquisitiones Arithmeticae'
    ])
);

newBookList 應等於 ["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae", "A Brief History of Time"].

assert(
  JSON.stringify(newBookList) ===
    JSON.stringify([
      'The Hound of the Baskervilles',
      'On The Electrodynamics of Moving Bodies',
      'Philosophiæ Naturalis Principia Mathematica',
      'Disquisitiones Arithmeticae',
      'A Brief History of Time'
    ])
);

newerBookList 應等於 ["The Hound of the Baskervilles", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"].

assert(
  JSON.stringify(newerBookList) ===
    JSON.stringify([
      'The Hound of the Baskervilles',
      'Philosophiæ Naturalis Principia Mathematica',
      'Disquisitiones Arithmeticae'
    ])
);

newestBookList 應等於 ["The Hound of the Baskervilles", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae", "A Brief History of Time"].

assert(
  JSON.stringify(newestBookList) ===
    JSON.stringify([
      'The Hound of the Baskervilles',
      'Philosophiæ Naturalis Principia Mathematica',
      'Disquisitiones Arithmeticae',
      'A Brief History of Time'
    ])
);

--seed--

--seed-contents--

// The global variable
var bookList = ["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"];

// Change code below this line
function add (bookName) {

  bookList.push(bookName);
  return bookList;

  // Change code above this line
}

// Change code below this line
function remove (bookName) {
  var book_index = bookList.indexOf(bookName);
  if (book_index >= 0) {

    bookList.splice(book_index, 1);
    return bookList;

    // Change code above this line
    }
}

var newBookList = add(bookList, 'A Brief History of Time');
var newerBookList = remove(bookList, 'On The Electrodynamics of Moving Bodies');
var newestBookList = remove(add(bookList, 'A Brief History of Time'), 'On The Electrodynamics of Moving Bodies');

console.log(bookList);

--solutions--

// The global variable
var bookList = ["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"];

function add (bookList, bookName) {
  return [...bookList, bookName];
}

function remove (bookList, bookName) {
  const bookListCopy = [...bookList];
  const bookNameIndex = bookList.indexOf(bookName);
  if (bookNameIndex >= 0) {
    bookListCopy.splice(bookNameIndex, 1);
  }
  return bookListCopy;
}

var newBookList = add(bookList, 'A Brief History of Time');
var newerBookList = remove(bookList, 'On The Electrodynamics of Moving Bodies');
var newestBookList = remove(add(bookList, 'A Brief History of Time'), 'On The Electrodynamics of Moving Bodies');