各种网页尺寸判断方法

function reachBottom() {
var scrollTop = 0;
var clientHeight = 0;
var scrollHeight = 0;
if (document.documentElement && document.documentElement.scrollTop) {
scrollTop = document.documentElement.scrollTop;
} else if (document.body) {
scrollTop = document.body.scrollTop;
}
if (document.body.clientHeight && document.documentElement.clientHeight) {
clientHeight = (document.body.clientHeight < document.documentElement.clientHeight) ? document.body.clientHeight: document.documentElement.clientHeight;
} else {
clientHeight = (document.body.clientHeight > document.documentElement.clientHeight) ? document.body.clientHeight: document.documentElement.clientHeight;
}
scrollHeight = Math.max(document.body.scrollHeight, document.documentElement.scrollHeight);
if (scrollTop + clientHeight == scrollHeight) {
return true;
} else {
return false;
}
}