关于viewport兼容性问题的实例代码

<meta id="viewport" content="
    target-densitydpi=device-dpi, 
    user-scalable=no, 
    width=device-width, 
    initial-scale=0.5" name="viewport" />

var viewPortScale;
var dpr = window.devicePixelRatio;
if(dpr <= 2) {
    viewPortScale = 1 / window.devicePixelRatio;
} else {
    viewPortScale = 0.5
}

document.getElementById('viewport').setAttribute(
        'content', 
        'user-scalable=no, 
         width=device-width, 
        initial-scale=' + viewPortScale);

// alert(viewPortScale);