js判断是否微信PC端打开内置浏览器

function isWeChat(){
    var ua = window.navigator.userAgent.toLowerCase();
    if(ua.match(/MicroMessenger/i) == 'micromessenger'){
        var system = {
            win: false,
            mac: false
        };
        //检测平台
        var p = navigator.platform;
        system.win = p.indexOf("Win") == 0;
        system.mac = p.indexOf("Mac") == 0;
        if (system.win || system.mac) {
            alert("在微信PC端上打开内置浏览器");     
        }else {
            alert("非微信PC端上打开内置浏览器");
        }
}