js全选代码

<input type="checkbox" id="selectAll"> 全选
<br>
<input type="checkbox" class="item"> 选项1
<input type="checkbox" class="item"> 选项2
<input type="checkbox" class="item"> 选项3
<!-- 更多选项 -->

document.getElementById('selectAll').addEventListener('change', function() {
    var checkboxes = document.getElementsByClassName('item');
    for (var i = 0; i < checkboxes.length; i++) {
        checkboxes[i].checked = this.checked;
    }
});

// 可选：当所有子项都被选中时，全选框也自动选中
var items = document.getElementsByClassName('item');
for (var i = 0; i < items.length; i++) {
    items[i].addEventListener('change', function() {
        var allChecked = true;
        for (var j = 0; j < items.length; j++) {
            if (!items[j].checked) {
                allChecked = false;
                break;
            }
        }
        document.getElementById('selectAll').checked = allChecked;
    });
}