Javascript .reduce() 提示？有没有办法重命名 \'undefined\' 组？答案

【问题标题】：Javascript .reduce() tips? Is there a way to rename 'undefined' group?Javascript .reduce() 提示？有没有办法重命名 \'undefined\' 组？
【发布时间】：2022-08-11 15:58:46
【问题描述】：

我试图了解.reduce() 函数以及执行以下操作的最佳方法。

我有以下代码：

const products = [
  { name: \'apples\', category: \'fruits\' },
  { name: \'oranges\', category: \'fruits\' },
  { name: \'potatoes\', category: \'vegetables\' }
];

const groupByCategory = products.reduce((group, product) => {
  const { category } = product;
  group[category] = group[category] ?? [];
  group[category].push(product);
  return group;
}, {});

我想添加一个没有 \'category\' 属性的产品，并且我希望它被推送到一个特定的键中，而不是被分组到 \"undefined\" 中，所以我将它编辑为：

const products = [
  { name: \"apples\", category: \"fruits\" },
  { name: \"oranges\", category: \"fruits\" },
  { name: \"potatoes\", category: \"vegetables\" },
  { name: \"guava\"}
];

const groupByCategory = products.reduce((group, product) => {

  const { category } = product ;

  // check if \'category\' exists, if it doesn\'t store it as an empty array to push to
  group[category] = group[category] ?? []; 
  
  // if category is undefined, push it into \'nocategory\'. Otherwise push into relevant.
  if(!category){
     group[\'nocategory\'].push(product);
  } else {
    group[category].push(product);
  };
  return group;
}, {\'nocategory\':[]});

console.log(JSON.stringify(groupByCategory, null, 2));

在大多数情况下，它可以工作（仍然有一个“未定义”组，但至少该对象被推入正确的组）。

我确信有更好的解决方案/正确的方法来做到这一点。任何指针将不胜感激。

标签： javascript reduce simplify

【解决方案1】：

你在这里创建未定义

group[category] = group[category] ?? []; // category can be undefined

将创建移到 if-else 语句中

const products = [
  { name: "apples", category: "fruits" },
  { name: "oranges", category: "fruits" },
  { name: "potatoes", category: "vegetables" },
  { name: "guava"}
];

const groupByCategory = products.reduce((group, product) => {

  const { category } = product ;

  // check if 'category' exists, if it doesn't store it as an empty array to push to
  // removed
  
  // if category is undefined, push it into 'nocategory'. Otherwise push into relevant.
  if(!category){
     group['nocategory'].push(product);
  } else {
    group[category] = group[category] ?? [] // HERE
    group[category].push(product);
  };
  return group;
}, {'nocategory':[]});

console.log(JSON.stringify(groupByCategory, null, 2));

【讨论】：