滚动后如何检查元素是否可见？

Simple modification for scrollable div (container)

var isScrolledIntoView = function(elem, container) {
    var containerHeight = $(container).height();
    var elemTop = $(elem).position().top;
    var elemBottom = elemTop + $(elem).height();
    return (elemBottom > 0 && elemTop < containerHeight);
}

NOTE: this does not work if the element is larger than the scrollable div.

This method will return true if any part of the element is visible on the page. It worked better in my case and may help someone else.

function isOnScreen(element) {
  var elementOffsetTop = element.offset().top;
  var elementHeight = element.height();

  var screenScrollTop = $(window).scrollTop();
  var screenHeight = $(window).height();

  var scrollIsAboveElement = elementOffsetTop + elementHeight - screenScrollTop >= 0;
  var elementIsVisibleOnScreen = screenScrollTop + screenHeight - elementOffsetTop >= 0;

  return scrollIsAboveElement && elementIsVisibleOnScreen;
}

A more efficient version of this answer:

 /**
 * Is element within visible region of a scrollable container
 * @param {HTMLElement} el - element to test
 * @returns {boolean} true if within visible region, otherwise false
 */
 function isScrolledIntoView(el) {
      var rect = el.getBoundingClientRect();
      return (rect.top >= 0) && (rect.bottom <= window.innerHeight);
 }

I have written a component for the task, designed to handle large numbers of elements extremely fast (to the tune of <10ms for 1000 elements on a slow mobile).

It works with every type of scroll container you have access to – window, HTML elements, embedded iframe, spawned child window – and is very flexible in what it detects (full or partial visibility, border box or content box, custom tolerance zone, etc).

A huge, mostly auto-generated test suite ensures that it works as advertised, cross-browser.

Give it a shot if you like: jQuery.isInView. Otherwise, you might find inspiration in the source code, e.g. here.

An example based off of this answer to check if an element is 75% visible (i.e. less than 25% of it is off of the screen).

function isScrolledIntoView(el) {
  // check for 75% visible
  var percentVisible = 0.75;
  var elemTop = el.getBoundingClientRect().top;
  var elemBottom = el.getBoundingClientRect().bottom;
  var elemHeight = el.getBoundingClientRect().height;
  var overhang = elemHeight * (1 - percentVisible);

  var isVisible = (elemTop >= -overhang) && (elemBottom <= window.innerHeight + overhang);
  return isVisible;
}

I have such a method in my application, but it does not use 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));
}

Edit : This method works well for I.E. (at least version 6). Read the comments for compatibility with FF.

function isScrolledIntoView(elem) {
    var docViewTop = $(window).scrollTop(),
        docViewBottom = docViewTop + $(window).height(),
        elemTop = $(elem).offset().top,
     elemBottom = elemTop + $(elem).height();
   //Is more than half of the element visible
   return ((elemTop + ((elemBottom - elemTop)/2)) >= docViewTop && ((elemTop + ((elemBottom - elemTop)/2)) <= docViewBottom));
}

isScrolledIntoView是一个非常需要的函数，因此我尝试了它，它适用于不比视口高的元素，但是如果该元素较大，则视口不起作用。要解决此问题，请轻松更改条件

return ((elemBottom <= docViewBottom) && (elemTop >= docViewTop));

对此：

return (docViewBottom >= elemTop && docViewTop <= elemBottom);

在此处查看演示：http : //jsfiddle.net/RRSmQ/

这里的大多数答案都没有考虑到元素也可以隐藏，因为它滚动到div的视图之外，不仅滚动到整个页面。

为了解决这种可能性，您基本上必须检查元素是否位于其每个父元素的边界内。

该解决方案正是这样做的：

function(element, percentX, percentY){
    var tolerance = 0.01;   //needed because the rects returned by getBoundingClientRect provide the position up to 10 decimals
    if(percentX == null){
        percentX = 100;
    }
    if(percentY == null){
        percentY = 100;
    }

    var elementRect = element.getBoundingClientRect();
    var parentRects = [];

    while(element.parentElement != null){
        parentRects.push(element.parentElement.getBoundingClientRect());
        element = element.parentElement;
    }

    var visibleInAllParents = parentRects.every(function(parentRect){
        var visiblePixelX = Math.min(elementRect.right, parentRect.right) - Math.max(elementRect.left, parentRect.left);
        var visiblePixelY = Math.min(elementRect.bottom, parentRect.bottom) - Math.max(elementRect.top, parentRect.top);
        var visiblePercentageX = visiblePixelX / elementRect.width * 100;
        var visiblePercentageY = visiblePixelY / elementRect.height * 100;
        return visiblePercentageX + tolerance > percentX && visiblePercentageY + tolerance > percentY;
    });
    return visibleInAllParents;
};

它还可以让您指定在每个方向上可见的百分比。
它没有涵盖由于其他因素（例如）可能将其隐藏的可能性display: hidden。

这应该在所有主流浏览器中都可以使用，因为它仅使用getBoundingClientRect。我亲自在Chrome和Internet Explorer 11中对其进行了测试。

对于我的需求，Tweeked的Scott Dowding很酷的功能-用于查找元素是否刚刚滚动到屏幕（即它的顶部边缘）中。

function isScrolledIntoView(elem)
{
    var docViewTop = $(window).scrollTop();
    var docViewBottom = docViewTop + $(window).height();
    var elemTop = $(elem).offset().top;
    return ((elemTop <= docViewBottom) && (elemTop >= docViewTop));
}

香草的答案：

function isScrolledIntoView(el) {
    var rect = el.getBoundingClientRect();
    var elemTop = rect.top;
    var elemBottom = rect.bottom;

    // Only completely visible elements return true:
    var isVisible = (elemTop >= 0) && (elemBottom <= window.innerHeight);
    // Partially visible elements return true:
    //isVisible = elemTop < window.innerHeight && elemBottom >= 0;
    return isVisible;
}

这是我的纯JavaScript解决方案，如果它也隐藏在可滚动容器内，则可以使用。

此处演示（也尝试调整窗口大小）

var visibleY = function(el){
  var rect = el.getBoundingClientRect(), top = rect.top, height = rect.height, 
    el = el.parentNode
  // Check if bottom of the element is off the page
  if (rect.bottom < 0) return false
  // Check its within the document viewport
  if (top > document.documentElement.clientHeight) return false
  do {
    rect = el.getBoundingClientRect()
    if (top <= rect.bottom === false) return false
    // Check if the element is out of view due to a container scrolling
    if ((top + height) <= rect.top) return false
    el = el.parentNode
  } while (el != document.body)
  return true
};

EDIT 2016-03-26：我已经更新了解决方案，以解决滚动到元素上方的问题，因此该元素隐藏在可滚动容器顶部的上方。 EDIT 2018-10-08：更新为在屏幕上方滚动出视图时进行处理。