1 javascript class classname selector queryselector
function name() {
    const select = document.querySelector("#id");
    select.classname = ("customclass")
}
我已经写了这段代码。但我无法更改类名。
您需要更改className属性:
const select = document. querySelector("#id"); 
select.className = "customclass";
console.log(select);<div id="id"></div>另一种方法是将其添加到classList评论中建议的内容中:
const select = document. querySelector("#id"); 
select.classList.add("customclass");
console.log(select);<div id="id"></div>