登录模板的第三方登录问题

if (~authBtns.indexOf(service.id)) {
var isInstalled = app.isInstalled(service.id);
var btn = document.createElement('div');
//如果微信未安装，则为不启用状态
btn.setAttribute('class', 'oauth-btn' + (!isInstalled && service.id === 'weixin' ? (' disabled') : ''));
btn.authId = service.id;
btn.style.backgroundImage = 'url("images/' + service.id + '.png")'
oauthArea.appendChild(btn);
}
问下 if里的波浪线啥意思啊？