SOURCE

// 补全代码
let all = document.querySelector('#all');
let options = Array.from(document.querySelectorAll('.item'));
all.onchange = function () {
    options.forEach(x => x.checked = all.checked)
}
options.onchange = function(){
        console.log(options)
}

<ul>
	<li>全选<input type='checkbox' id='all'></li>
    <li>Java<input type='checkbox' class='item'></li>
    <li>javaScript<input type='checkbox' class='item'></li>
    <li>C++<input type='checkbox' class='item'></li>
    <li>python<input type='checkbox' class='item'></li>
    <li>.net<input type='checkbox' class='item'></li>
</ul>