js给按钮加背景颜色

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Button Color Change</title>
</head>
<body>
    <button id="myButton">Click Me</button>

    <script>
        // 获取按钮元素
        var button = document.getElementById('myButton');
        // 设置背景颜色
        button.style.backgroundColor = 'blue';
    </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Button Color Change</title>
    <style>
        .colored-button {
            background-color: green;
        }
    </style>
</head>
<body>
    <button id="myButton">Click Me</button>

    <script>
        // 获取按钮元素
        var button = document.getElementById('myButton');
        // 添加class
        button.classList.add('colored-button');
    </script>
</body>
</html>

window.onload = function() {
    var button = document.getElementById('myButton');
    button.style.backgroundColor = 'blue';
};