js判断是否是微信浏览器

<script type="text/javascript">
window.onload = function(){
    if(isWeiXin()){
        var p = document.getElementsByTagName('p');
        p[0].innerHTML = window.navigator.userAgent;
    }
}
function isWeiXin(){
    var ua = window.navigator.userAgent.toLowerCase();
    if(ua.match(/MicroMessenger/i) == 'micromessenger'){
        return true;
    }else{
        return false;
    }
}
</script>