使用 jquery 获取元素相对于 viewport 的位置

查看维度插件，特别是 scrollTop()/scrollLeft()。信息可以在 http://api.jquery.com/scrollTop找到。

这里有两个函数可以在不使用(臃肿的)尺寸插件的情况下获得页面高度和滚动量(x，y) :

// getPageScroll() by quirksmode.com
function getPageScroll() {
var xScroll, yScroll;
if (self.pageYOffset) {
yScroll = self.pageYOffset;
xScroll = self.pageXOffset;
} else if (document.documentElement && document.documentElement.scrollTop) {
yScroll = document.documentElement.scrollTop;
xScroll = document.documentElement.scrollLeft;
} else if (document.body) {// all other Explorers
yScroll = document.body.scrollTop;
xScroll = document.body.scrollLeft;
}
return new Array(xScroll,yScroll)
}


// Adapted from getPageSize() by quirksmode.com
function getPageHeight() {
var windowHeight
if (self.innerHeight) { // all except Explorer
windowHeight = self.innerHeight;
} else if (document.documentElement && document.documentElement.clientHeight) {
windowHeight = document.documentElement.clientHeight;
} else if (document.body) { // other Explorers
windowHeight = document.body.clientHeight;
}
return windowHeight
}

确定元素的大小和位置的最简单方法是调用 这个方法返回视口坐标中的元素位置，它不需要参数并返回一个带有 属性 left, right, top和 底部 元素左上角的坐标以及右下角的属性 给出右下角的坐标。

我发现 cballou 的答案从2014年1月起就不再适用于 Firefox 了。具体来说，如果客户端滚动正确，则 if (self.pageYOffset)不会触发，但不会向下滚动——因为 0是一个假数字。由于 Firefox 支持 document.body.scrollLeft/Top，这个问题在一段时间内没有被发现，但是这个问题已经不再适用于我(在 Firefox 26.0上)。

这是我修改后的解决方案:

var getPageScroll = function(document_el, window_el) {
var xScroll = 0, yScroll = 0;
if (window_el.pageYOffset !== undefined) {
yScroll = window_el.pageYOffset;
xScroll = window_el.pageXOffset;
} else if (document_el.documentElement !== undefined && document_el.documentElement.scrollTop) {
yScroll = document_el.documentElement.scrollTop;
xScroll = document_el.documentElement.scrollLeft;
} else if (document_el.body !== undefined) {// all other Explorers
yScroll = document_el.body.scrollTop;
xScroll = document_el.body.scrollLeft;
}
return [xScroll,yScroll];
};

在 FF26，Chrome31，IE11中测试和工作。几乎可以肯定的是，所有这些浏览器的老版本都可以工作。

jQuery.offset 需要与 scrollTop和 scrollLeft结合，如下图所示:

演示:

function getViewportOffset($e) {
var $window = $(window),
scrollLeft = $window.scrollLeft(),
scrollTop = $window.scrollTop(),
offset = $e.offset(),
rect1 = { x1: scrollLeft, y1: scrollTop, x2: scrollLeft + $window.width(), y2: scrollTop + $window.height() },
rect2 = { x1: offset.left, y1: offset.top, x2: offset.left + $e.width(), y2: offset.top + $e.height() };
return {
left: offset.left - scrollLeft,
top: offset.top - scrollTop,
insideViewport: rect1.x1 < rect2.x2 && rect1.x2 > rect2.x1 && rect1.y1 < rect2.y2 && rect1.y2 > rect2.y1
};
}
$(window).on("load scroll resize", function() {
var viewportOffset = getViewportOffset($("#element"));
$("#log").text("left: " + viewportOffset.left + ", top: " + viewportOffset.top + ", insideViewport: " + viewportOffset.insideViewport);
});

body { margin: 0; padding: 0; width: 1600px; height: 2048px; background-color: #CCCCCC; }
#element { width: 384px; height: 384px; margin-top: 1088px; margin-left: 768px; background-color: #99CCFF; }
#log { position: fixed; left: 0; top: 0; font: medium monospace; background-color: #EEE8AA; }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>


<!-- scroll right and bottom to locate the blue square -->
<div id="element"></div>
<div id="log"></div>

Here is a function that calculates the current position of an element within the viewport:

/**
* Calculates the position of a given element within the viewport
*
* @param {string} obj jQuery object of the dom element to be monitored
* @return {array} An array containing both X and Y positions as a number
* ranging from 0 (under/right of viewport) to 1 (above/left of viewport)
*/
function visibility(obj) {
var winw = jQuery(window).width(), winh = jQuery(window).height(),
elw = obj.width(), elh = obj.height(),
o = obj[0].getBoundingClientRect(),
x1 = o.left - winw, x2 = o.left + elw,
y1 = o.top - winh, y2 = o.top + elh;


return [
Math.max(0, Math.min((0 - x1) / (x2 - x1), 1)),
Math.max(0, Math.min((0 - y1) / (y2 - y1), 1))
];
}

The return values are calculated like this:

用法:

visibility($('#example'));  // returns [0.3742887830933581, 0.6103752759381899]

演示:

function visibility(obj) {var winw = jQuery(window).width(),winh = jQuery(window).height(),elw = obj.width(),
elh = obj.height(), o = obj[0].getBoundingClientRect(),x1 = o.left - winw, x2 = o.left + elw, y1 = o.top - winh, y2 = o.top + elh; return [Math.max(0, Math.min((0 - x1) / (x2 - x1), 1)),Math.max(0, Math.min((0 - y1) / (y2 - y1), 1))];
}
setInterval(function() {
res = visibility($('#block'));
$('#x').text(Math.round(res[0] * 100) + '%');
$('#y').text(Math.round(res[1] * 100) + '%');
}, 100);

#block { width: 100px; height: 100px; border: 1px solid red; background: yellow; top: 50%; left: 50%; position: relative;
} #container { background: #EFF0F1; height: 950px; width: 1800px; margin-top: -40%; margin-left: -40%; overflow: scroll; position: relative;
} #res { position: fixed; top: 0; z-index: 2; font-family: Verdana; background: #c0c0c0; line-height: .1em; padding: 0 .5em; font-size: 12px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="res">
<p>X: <span id="x"></span></p>
<p>Y: <span id="y"></span></p>
</div>
<div id="container"><div id="block"></div></div>