js判断手机型号

由于oppo手机自带浏览器的高度底部多了144px导航栏

所以：专门针对oppo手机做适配：

var dowphone = document.getElementById("dowphone");
function validBrowser(){   
    var u_agent = navigator.userAgent;    
    if(u_agent.indexOf(\'OPPO R7s Build\')>-1){   
        dowphone.style.width = "54%";
        dowphone.style.marginLeft = "-27%";
    } 
}  
validBrowser();