javascript - 怎么找没有。名称为 "myDIV"的类？

Question

这个问题已经有答案了:

How can I count the number of elements with same class? (6 个回答)

已关闭 5 年前。

/*请查看这段代码并告诉我如何找到 no。类“myDIV”我也尝试过 getelementbyid 和 childNodes.length 但没有任何效果*/

<div id="example">First div element with class="example"
    <div class="fexample">First div element with class="example"
    <div class="myDIV">
      <p>First p element in div.</p>
      <p>Another p element in div.</p>
    </div>
    <div class="myDIV">
      <p>First p element in div.</p>
      <p>Another p element in div.</p>
    </div>
    <div class="myDIV">
      <p>First p element in div.</p>
      <p>Another p element in div.</p>
    </div>
    </div>
    </div>
    <script>
     function myFunction() {
     var a = document.getElementsByClassName("myDIV");
     document.getElementById("demo").innerHTML = a.length;
    }
    </script>
        </body>

Answer 1

使用document.querySelectorAll()要构建包含该类的所有元素的列表，请使用 .length 属性返回金额。

var elements = document.querySelectorAll('.myDIV');
console.log(elements.length)

<div id="example">First div element with class="example"
    <div class="fexample">First div element with class="example"
    <div class="myDIV">
      <p>First p element in div.</p>
      <p>Another p element in div.</p>
    </div>
    <div class="myDIV">
      <p>First p element in div.</p>
      <p>Another p element in div.</p>
    </div>
    <div class="myDIV">
      <p>First p element in div.</p>
      <p>Another p element in div.</p>
    </div>
    </div>
    </div>