我通过AJAX加载元素。其中一些只有当你向下滚动页面时才能看到。有什么方法可以知道元素现在是否在页面的可见部分?
当前回答
仅限Javascript:)
function isInViewport(element) {
var rect = element.getBoundingClientRect();
var html = document.documentElement;
return (
rect.top >= 0 &&
rect.left >= 0 &&
rect.bottom <= (window.innerHeight || html.clientHeight) &&
rect.right <= (window.innerWidth || html.clientWidth)
);
}
其他回答
我在我的应用程序中有这样一个方法,但它不使用jQuery:
/* Get the TOP position of a given element. */
function getPositionTop(element){
var offset = 0;
while(element) {
offset += element["offsetTop"];
element = element.offsetParent;
}
return offset;
}
/* Is a given element is visible or not? */
function isElementVisible(eltId) {
var elt = document.getElementById(eltId);
if (!elt) {
// Element not found.
return false;
}
// Get the top and bottom position of the given element.
var posTop = getPositionTop(elt);
var posBottom = posTop + elt.offsetHeight;
// Get the top and bottom position of the *visible* part of the window.
var visibleTop = document.body.scrollTop;
var visibleBottom = visibleTop + document.documentElement.offsetHeight;
return ((posBottom >= visibleTop) && (posTop <= visibleBottom));
}
编辑:此方法适用于I.E.(至少版本6)。请阅读评论以了解FF的兼容性。
我只是想分享一下,我把这个和我的脚本结合起来移动div,这样它就总是在视图中:
$("#accordion").on('click', '.subLink', function(){
var url = $(this).attr('src');
updateFrame(url);
scrollIntoView();
});
$(window).scroll(function(){
changePos();
});
function scrollIntoView()
{
var docViewTop = $(window).scrollTop();
var docViewBottom = docViewTop + $(window).height();
var elemTop = $("#divPos").offset().top;
var elemBottom = elemTop + $("#divPos").height();
if (elemTop < docViewTop){
$("#divPos").offset({top:docViewTop});
}
}
function changePos(){
var scrTop = $(window).scrollTop();
var frmHeight = $("#divPos").height()
if ((scrTop < 200) || (frmHeight > 800)){
$("#divPos").attr("style","position:absolute;");
}else{
$("#divPos").attr("style","position:fixed;top:5px;");
}
}
其他答案通常不检查元素是否在视图中沿着X轴,即可能在当前视口Y范围内,但不在X范围内。这个函数检查X和Y是否显示在视口中:
function checkElInView(el) {
if (!el || !typeof el.getBoundingClientRect === "function") return false;
const r = el.getBoundingClientRect();
const vw = document.documentElement.clientWidth;
const vh = document.documentElement.clientHeight;
const inViewX = (r.left > 0 && r.left < vw) || (r.right < vw && r.right > 0);
const inViewY = (r.top > 0 && r.top < vh) || (r.bottom < vh && r.bottom > 0);
return inViewX && inViewY;
}
简单的检查元素(el)是否在可滚动的div (holder)中可见
function isElementVisible (el, holder) {
holder = holder || document.body
const { top, bottom, height } = el.getBoundingClientRect()
const holderRect = holder.getBoundingClientRect()
return top <= holderRect.top
? holderRect.top - top <= height
: bottom - holderRect.bottom <= height
}
使用jQuery:
var el = $('tr:last').get(0);
var holder = $('table').get(0);
var isVisible = isElementVisible(el, holder);
我们可以在使用ES6的现代浏览器中做这样的事情:
const isFullySeen = el => el &&
typeof el.getBoundingClientRect === 'function' &&
el.getBoundingClientRect()['bottom'] + window.scrollY <=
window.innerHeight + window.scrollY &&
el.getBoundingClientRect()['top'] + window.scrollY <=
window.innerHeight + window.scrollY;