W3School TIY Editor
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<!DOCTYPE html> <html> <style> .myStyle { background-color: coral; padding: 16px; } .anotherClass { text-align: center; font-size: 25px; } .thirdClass { text-transform: uppercase; } </style> <body> <h1>DOMToken 对象</h1> <h2>length 属性</h2> <div id="myDIV" class="myStyle anotherClass thirdClass"> <p>I am a myDIV.</p> </div> <p>myDIV 中的类名数量为：</p> <p id="demo"></p> <script> let numb = document.getElementById("myDIV").classList.length; document.getElementById("demo").innerHTML = numb; </script> </body> </html>