获取页面视口大小
let pageWidth = window.innerWidth,
pageHeigth = window.innerHeight;
if(typeof pageWidth !== 'number') {
if(document.compatMode == "CSS1Compat") {
pageWidth = document.documentElement.clientWidth;
pageHeigth = document.documentElement.clientHeight;
} else {
pageWidth = document.body.clientWidth;
pageHeigth = document.body.clientHeight;
}
}