检查空/未定义的更好方法

Question

我想知道我能不能升级我的代码。我有以下步骤:当找不到标题时，就找不到一本书。当找不到一本书的部分元数据时，这本书仍然可用，但是请求的数据应该以未知的形式返回。

var notAvailableMSG = process.env.notAvailableMSG;
var unknownMSG = process.env.unknownMSG;
var bookInfo = [];

// if title is not found = book is not available.
if(bookInfo.title == '' || bookInfo.title == undefined ){
  bookInfo.isbn = isbn;
  bookInfo.title = notAvailableMSG;
  bookInfo.author = notAvailableMSG;
  bookInfo.publisher = notAvailableMSG;
  bookInfo.price = notAvailableMSG;
  bookInfo.currency = notAvailableMSG;
  bookInfo.url = notAvailableMSG;
  bookInfo.releasedate = notAvailableMSG;
  bookInfo.sellable = notAvailableMSG;
}
// Check for other empty values
if(bookInfo.author == '' || bookInfo.author == undefined){
  bookInfo.author = unknownMSG;
}
if(bookInfo.publisher == '' || publisher == undefined){
  bookInfo.publisher = unknownMSG;
}
if(bookInfo.price == '' || bookInfo.price == undefined){
  bookInfo.price = unknownMSG;
}
if(bookInfo.releasedate == '' || bookInfo.releasedate == undefined){
  bookInfo.releasedate = unknownMSG;
}

这段代码能否以更好的方式编写，让这段代码运行得更快(使其更易读)？

Answer 1

当我有长长的属性列表时，如果可能的话，我更喜欢避免重复的代码或重复的if。

在这种情况下，我会使用如下内容：

var properties = [
  'author',
  'publisher',
  'price',
  'currency',
  'url',
  'releasedate',
  'sellable'
];

if(!bookInfo.title) {
  bookInfo.isbn = isbn;
  bookInfo.title = notAvailableMSG;
  properties.map(function(prop) {
    bookInfo[prop] = notAvailableMSG;
  });
}

// Check for other empty values
properties.map(function(prop) {
  if(!bookInfo[prop]) {
    bookInfo[prop] = unknownMSG;
  }
});

Answer 2

我认为检查一个值是否为空的最简单的方法是检查它是否是虚假的。它不是最快的代码，但在我看来更容易读懂：

if(!bookInfo.author){
  bookInfo.author = unknownMSG;
}
if(!bookInfo.publisher){
  bookInfo.publisher = unknownMSG;
}
if(!bookInfo.price && bookInfo.price !== 0){
  bookInfo.price = unknownMSG;
}
if(!bookInfo.releasedate){
  bookInfo.releasedate = unknownMSG;
}

您可以检查this post，以查看JS中的值何时为虚值：

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编辑

正如H.B.所说，您可以使用一个函数来检查书中的每个键。此外，如果要检查对象的每个键，也可以使用Object.keys：

['author', 'publisher', 'price', 'releasedate', /* ... */].forEach(key => {
  if (bookInfo[key] === undefined || bookInfo[key] === null || bookInfo[key] === '') {
    bookInfo[key] = unknownMSG;
  }
});

Answer 3

另一种可能的重构：

const checkUnknown = prop => {
  if(bookInfo[prop] == '' || bookInfo[prop] == undefined){
    bookInfo[prop] = unknownMSG;
  }
}
checkUnknown('author');
checkUnknown('publisher');
checkUnknown('price');
checkUnknown('releasedate');

更花哨，考虑到标题：

const checkUnknown = (prop, customCallback) => {
  if (bookInfo[prop] == '' || bookInfo[prop] == undefined) {
    if (customCallback)
      customCallback();
    else
      bookInfo[prop] = unknownMSG;
  }
}
checkUnknown('author');
checkUnknown('publisher');
checkUnknown('price');
checkUnknown('releasedate');
checkUnknown('title', () => {
  bookInfo.isbn = isbn;
  bookInfo.title = notAvailableMSG;
  bookInfo.author = notAvailableMSG;
  bookInfo.publisher = notAvailableMSG;
  bookInfo.price = notAvailableMSG;
  bookInfo.currency = notAvailableMSG;
  bookInfo.url = notAvailableMSG;
  bookInfo.releasedate = notAvailableMSG;
  bookInfo.sellable = notAvailableMSG;
});