js全选反选

<input type="checkbox" id="selectAll"> 全选/反选
<br>
<input type="checkbox" class="item"> 选项1
<br>
<input type="checkbox" class="item"> 选项2
<br>
<input type="checkbox" class="item"> 选项3

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

// 反选功能
document.getElementById('selectAll').addEventListener('click', function() {
    this.checked = !this.checked; // 切换全选按钮的状态
    var checkboxes = document.getElementsByClassName('item');
    for (var i = 0; i < checkboxes.length; i++) {
        checkboxes[i].checked = !checkboxes[i].checked; // 切换每个复选框的状态
    }
});