在初始化和更改时检查选择框的值

<select id="mySelect">
    <option value="option1">Option 1</option>
    <option value="option2">Option 2</option>
    <option value="option3">Option 3</option>
</select>

document.addEventListener('DOMContentLoaded', function() {
    // 初始化时检查选择框的值
    checkSelectValue();

    // 更改时检查选择框的值
    document.getElementById('mySelect').addEventListener('change', checkSelectValue);
});

function checkSelectValue() {
    var selectElement = document.getElementById('mySelect');
    var selectedValue = selectElement.value;
    console.log('Selected Value:', selectedValue);

    // 根据选择的值执行相应的操作
    switch (selectedValue) {
        case 'option1':
            console.log('You selected Option 1');
            break;
        case 'option2':
            console.log('You selected Option 2');
            break;
        case 'option3':
            console.log('You selected Option 3');
            break;
        default:
            console.log('No option selected');
    }
}