var frees = document.getElementsByClassName('zhuanlan-subscribe-btn');
var free = [];
for (var i = 0; i < frees.length; i++) {
    var item = frees[i];
    var span = item.getElementsByTagName('span')[0]
    if (span.innerText == '免费订阅') {
        free.push(item)
    }
}

for (var i = 0; i < free.length; i++) {
    var item = free[i];
    var name = item.getAttribute('data-domain-name');
    var url = 'https://xiaozhuanlan.com/' + name + '/subscribe'
    var rq = new XMLHttpRequest();
    rq.open('GET', url, true)
    rq.send()
}