如何 select 多个块的每个第一项 (html, javascript)

Question

我正在尝试 select 一系列多个块中的每个第一项，但我不知道该怎么做 :(

这是我尝试过的一个例子：

let everyItems = Array.from(document.querySelectorAll('.block .item'));
let firstItems = Array.from(everyItems[0]);

document.getElementById('every1stItem').innerText = firstItems.innerText;

<div calss="block"><b>First block</b>
  <div class="item">Item 1.1</div>
  <div class="item">Item 1.2</div>
  <div class="item">Item 1.3</div>
  <div class="item">Item 1.4</div>
 </div>
 <div calss="block"><b>Second block</b>
  <div class="item">Item 2.1</div>
  <div class="item">Item 2.2</div>
  <div class="item">Item 2.3</div>
  <div class="item">Item 2.4</div>
 </div>
 <div calss="block"><b>Third block</b>
  <div class="item">Item 3.1</div>
  <div class="item">Item 3.2</div>
  <sdivan class="item">Item 3.3</div>
  <div class="item">Item 3.4</div>
 </div>
 
 <div>
  <b>The first item of every block is :</b>
  <div id="every1stItem"></div>
 </div>
 
 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

谢谢你帮助我！

Answer 1

你可以这样做

let everyItems = Array.from(document.querySelectorAll('.block'));

let firstItems = everyItems.map(i => i.children[1].innerText).join(', ')

document.getElementById('every1stItem').innerText = firstItems;

<div class="block"><b>First block</b>
  <div class="item">Item 1.1</div>
  <div class="item">Item 1.2</div>
  <div class="item">Item 1.3</div>
  <div class="item">Item 1.4</div>
 </div>
 <div class="block"><b>Second block</b>
  <div class="item">Item 2.1</div>
  <div class="item">Item 2.2</div>
  <div class="item">Item 2.3</div>
  <div class="item">Item 2.4</div>
 </div>
 <div class="block"><b>Third block</b>
  <div class="item">Item 3.1</div>
  <div class="item">Item 3.2</div>
  <div class="item">Item 3.3</div>
  <div class="item">Item 3.4</div>
 </div>
 
 <div>
  <b>The first item of every block is :</b>
  <div id="every1stItem"></div>
 </div>
 
 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

Answer 2

使用 :nth-child(n) 选择器

let everyItems = $('.item:nth-child(2)');
$('#every1stItem').html(everyItems)

<div>
  <b>The first item of every block is :</b>
  <div id="every1stItem"></div>
</div>
<hr>
<div class="block"><b>First block</b>
  <div class="item">Item 1.1</div>
  <div class="item">Item 1.2</div>
  <div class="item">Item 1.3</div>
  <div class="item">Item 1.4</div>
</div>
<div class="block"><b>Second block</b>
  <div class="item">Item 2.1</div>
  <div class="item">Item 2.2</div>
  <div class="item">Item 2.3</div>
  <div class="item">Item 2.4</div>
</div>
<div class="block"><b>Third block</b>
  <div class="item">Item 3.1</div>
  <div class="item">Item 3.2</div>
  <div class="item">Item 3.3</div>
  <div class="item">Item 3.4</div>
</div>


 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

Answer 3

document.queryselector(".className") returns 第一个元素 class className

如何 select 多个块的每个第一项 (html, javascript)

How to select every first items of multiple blocks (html, javascript)

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arrays

selectors-api