SOURCE

// 切换
function switchRadio(btn) {
    var elem = document.getElementById('radio');
    if (elem.classList.contains('radio-selected') == true) {
        elem.classList.remove('radio-selected');
        btn.innerHTML='选中';
    } else {
        elem.classList.add('radio-selected');
        btn.innerHTML='反选';
    }
}

<div class="radio" id="radio"></div>

<hr />
<button onclick="switchRadio(this)">选中</button>

.radio {
    width: 32px;
    height: 32px;
    border-radius: 50%;
    border: 1px solid #777;
}

/* 用于动态添加的类 */
.radio-selected {
    background: red;
}