JSON-array 和 forEach 问题

Question

所以...根据控制台，我遇到的问题是： “未捕获的类型错误：无法读取未定义的属性“标题” 在 custom.js:42，在 Array.forEach ()，在 custom.js:39"

“标题”如何未定义？我的 .forEach 有什么问题？ （悲伤的声音）

我构建的 JSON 数组中六个对象中的第一个示例：

var  newReleases =  [   
    {
"title":"Honor - Defending the motherland",
"author":"Mark Thomas",
"genre":"Fiction",  
"description":"In legislation and formal documents the suffix shire was generally not used: for example, Bedfordshire was referred to as the administrative county of Bedford and the Northamptonshire council as the county council of Northampton.The 1888 Act did not contain a list of administrative counties: it was not until 1933 and the passing of a new Local Government Act."},

带有 forEach 函数的 For 循环：

for (var i = 0; i < 6; i++){
    
newReleases.forEach (function (newReleases) { 
    
var bookTitle = document.getElementsByClassName('card-header')
var t = document.createTextNode(newReleases[i].title);
bookTitle.appendChild(t);

var bookAuthor = document.getElementsByClassName('card-title')
var a = document.createTextNode(newReleases[i].authors);
bookAuthor.appendChild(a);

var cardGenre = document.getElementsByClassName("card-subtitle");
var genre = document.createTextNode(newReleases[i].genre);
cardGenre.appendChild(genre);   
    
    
var cardDescr = document.getElementsByClassName('card-text');
var p = document.createTextNode(newReleases[i].description);
cardDescr.appendChild(p);
        
    }) //end of forEach
} // end of for-loop

Answer 1

使用for 或forEach()，不能同时使用。

for (var i = 0; i < newReleases.length; i++) {
  var bookTitle = document.getElementsByClassName('card-header')[0]
  var t = document.createTextNode(newReleases[i].title);
  bookTitle.appendChild(t);

  var bookAuthor = document.getElementsByClassName('card-title')[0]
  var a = document.createTextNode(newReleases[i].authors);
  bookAuthor.appendChild(a);

  var cardGenre = document.getElementsByClassName("card-subtitle")[0];
  var genre = document.createTextNode(newReleases[i].genre);
  cardGenre.appendChild(genre);

  var cardDescr = document.getElementsByClassName('card-text')[0];
  var p = document.createTextNode(newReleases[i].description);
  cardDescr.appendChild(p);
}

或

newReleases.forEach(function(release) {
  var bookTitle = document.getElementsByClassName('card-header')[0]
  var t = document.createTextNode(release.title);
  bookTitle.appendChild(t);

  var bookAuthor = document.getElementsByClassName('card-title')[0]
  var a = document.createTextNode(release.authors);
  bookAuthor.appendChild(a);

  var cardGenre = document.getElementsByClassName("card-subtitle")[0];
  var genre = document.createTextNode(release.genre);
  cardGenre.appendChild(genre);

  var cardDescr = document.getElementsByClassName('card-text')[0];
  var p = document.createTextNode(release.description);
  cardDescr.appendChild(p);
});

当你使用forEach()时，你不需要下标数组变量，你只需使用回调函数的参数。