js判断页面放大缩小

// 若返回100则为默认无缩放，如果大于100则是放大，否则缩小
function detectZoom (){
var ratio = 0,
screen = window.screen,
ua = navigator.userAgent.toLowerCase();

if (window.devicePixelRatio !== undefined) {
ratio = window.devicePixelRatio;
}
else if (~ua.indexOf('msie')) {
if (screen.deviceXDPI && screen.logicalXDPI) {
ratio = screen.deviceXDPI / screen.logicalXDPI;
}
}
else if (window.outerWidth !== undefined && window.innerWidth !== undefined) {
ratio = window.outerWidth / window.innerWidth;
}

if (ratio){
ratio = Math.round(ratio * 100);
}

return ratio;
};