koa2判断移动端还是pc端

利用user-agent，判断请求是移动端的还是pc端的。

const checkPhone = (ctx) => {
    let userAgent = ctx.request.header['user-agent'].toLowerCase();
    let pat_phone = /ipad|iphone os|midp|rv:1.2.3.4|ucweb|android|windows ce|windows mobile/;
    return pat_phone.test(userAgent);
}