<!DOCTYPE html> <html> <style> .democlass {color:red} </style> <body> <h1>HTML DOM Attributes</h1> <h2>setNamedItem() 方法</h2> <p>将第一个 H1 的 class 属性设置为 "democlass"。</p> <script> const nodeMap = document.getElementsByTagName("H1")[0].attributes; const node = document.createAttribute("class"); node.value = "democlass"; nodeMap.setNamedItem(node); </script> </body> </html>