<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title></title> <style> div { height: 50px; width: 100px; margin-top: 10px; background-color: pink; } .cls { background-color: deeppink; } </style> </head> <body> <p class="cls">這是一個p</p> <p>這是另一個p</p> <span class="cls">這是一個span</span><br/> <span>這是另一個span</span><br/> <div class="cls">這是一個div</div> <div>這是另一個div</div> <input type="button" value="顯示效果" id="bt"/> <script src="common.js"></script> <script> //點擊按鈕設置應用cls類樣式的背景顏色為紅色 my$("bt").onclick = function () { var clsObjs = document.getElementsByClassName("cls"); for (var i = 0; i < clsObjs.length; i++) { clsObjs[i].style.backgroundColor = "red"; } }; </script> </body> </html>