Array.slice() 参数不是函数

Question

我在使用 freeCodeCamp beta 时遇到了一个奇怪的问题。

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这样做的“目的”不是修改原始数组，而是使用函数式编程技术来修改数组。

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然而，我不断收到关于“array”参数的抱怨，因为删除函数不是有效的函数：

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//  the global variable\nvar bookList = [\n    "The Hound of the Baskervilles",\n    "On The Electrodynamics of Moving Bodies",\n    "Philosophi\xc3\xa6 Naturalis Principia Mathematica",\n    "Disquisitiones Arithmeticae"];\n\n/* This function should add a book to the list and return the list */\n// New parameters should come before the bookName one\n\n// Add your code below this line\nfunction add (bookListTemp, bookName) {\n  let newBookArr = bookListTemp;\n  return newBookArr.push(bookName);\n  // Add your code above this line\n}\n\n/* This function should remove a book from the list and return the list */\n// New parameters should come before the bookName one\n\n// Add your code below this line\nfunction remove (bookList,bookName) {\n  let newArr = bookList.slice();\n  if (newArr.indexOf(bookName) >= 0) {\n\n    return newArr.slice(0, 1, bookName);\n\n    // Add your code above this line\n    }\n}\n\nvar newBookList = add(bookList, \'A Brief History of Time\');\nvar newerBookList = remove(bookList, \'On The Electrodynamics of Moving Bodies\');\nvar newestBookList = remove(add(bookList, \'A Brief History of Time\'),\n    \'On The Electrodynamics of Moving Bodies\');\n\nconsole.log(bookList);\n

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在删除函数中，我尝试获取参数并执行 array.slice() 方法以及 array.concat() 方法。自从做了let newArr = bookList实际上并没有使新数组正确吗？它只是创建一个引用原始数组的新副本，正确吗？

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我得到的确切错误是TypeError: bookList.slice is not a function

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更奇怪的是Array.isArray(bookList)返回true（在function remove. 所以我不明白为什么它抱怨数组方法？

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Answer 1

你的问题是Array.push

return 调用该方法的对象的新 length 属性。

你应该返回数组

function add (bookListTemp, bookName) {
      let newBookArr = bookListTemp;
      newBookArr.push(bookName);
      // Add your code above this line
      return newBookArr;
    }

或者 让我们尝试Array.concat代替

function add (bookListTemp, bookName) {
  let newBookArr = bookListTemp;
  return newBookArr.concat(bookName);
  // Add your code above this line
}