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

这里有一种使用Mootools实现相同目标的方法,可以是水平的、垂直的或两者都有。

Element.implement({
inVerticalView: function (full) {
    if (typeOf(full) === "null") {
        full = true;
    }

    if (this.getStyle('display') === 'none') {
        return false;
    }

    // Window Size and Scroll
    var windowScroll = window.getScroll();
    var windowSize = window.getSize();
    // Element Size and Scroll
    var elementPosition = this.getPosition();
    var elementSize = this.getSize();

    // Calculation Variables
    var docViewTop = windowScroll.y;
    var docViewBottom = docViewTop + windowSize.y;
    var elemTop = elementPosition.y;
    var elemBottom = elemTop + elementSize.y;

    if (full) {
        return ((elemBottom >= docViewTop) && (elemTop <= docViewBottom)
            && (elemBottom <= docViewBottom) && (elemTop >= docViewTop) );
    } else {
        return ((elemBottom <= docViewBottom) && (elemTop >= docViewTop));
    }
},
inHorizontalView: function(full) {
    if (typeOf(full) === "null") {
        full = true;
    }

    if (this.getStyle('display') === 'none') {
        return false;
    }

    // Window Size and Scroll
    var windowScroll = window.getScroll();
    var windowSize = window.getSize();
    // Element Size and Scroll
    var elementPosition = this.getPosition();
    var elementSize = this.getSize();

    // Calculation Variables
    var docViewLeft = windowScroll.x;
    var docViewRight = docViewLeft + windowSize.x;
    var elemLeft = elementPosition.x;
    var elemRight = elemLeft + elementSize.x;

    if (full) {
        return ((elemRight >= docViewLeft) && (elemLeft <= docViewRight)
            && (elemRight <= docViewRight) && (elemLeft >= docViewLeft) );
    } else {
        return ((elemRight <= docViewRight) && (elemLeft >= docViewLeft));
    }
},
inView: function(full) {
    return this.inHorizontalView(full) && this.inVerticalView(full);
}});

其他回答

这里有一种使用Mootools实现相同目标的方法,可以是水平的、垂直的或两者都有。

Element.implement({
inVerticalView: function (full) {
    if (typeOf(full) === "null") {
        full = true;
    }

    if (this.getStyle('display') === 'none') {
        return false;
    }

    // Window Size and Scroll
    var windowScroll = window.getScroll();
    var windowSize = window.getSize();
    // Element Size and Scroll
    var elementPosition = this.getPosition();
    var elementSize = this.getSize();

    // Calculation Variables
    var docViewTop = windowScroll.y;
    var docViewBottom = docViewTop + windowSize.y;
    var elemTop = elementPosition.y;
    var elemBottom = elemTop + elementSize.y;

    if (full) {
        return ((elemBottom >= docViewTop) && (elemTop <= docViewBottom)
            && (elemBottom <= docViewBottom) && (elemTop >= docViewTop) );
    } else {
        return ((elemBottom <= docViewBottom) && (elemTop >= docViewTop));
    }
},
inHorizontalView: function(full) {
    if (typeOf(full) === "null") {
        full = true;
    }

    if (this.getStyle('display') === 'none') {
        return false;
    }

    // Window Size and Scroll
    var windowScroll = window.getScroll();
    var windowSize = window.getSize();
    // Element Size and Scroll
    var elementPosition = this.getPosition();
    var elementSize = this.getSize();

    // Calculation Variables
    var docViewLeft = windowScroll.x;
    var docViewRight = docViewLeft + windowSize.x;
    var elemLeft = elementPosition.x;
    var elemRight = elemLeft + elementSize.x;

    if (full) {
        return ((elemRight >= docViewLeft) && (elemLeft <= docViewRight)
            && (elemRight <= docViewRight) && (elemLeft >= docViewLeft) );
    } else {
        return ((elemRight <= docViewRight) && (elemLeft >= docViewLeft));
    }
},
inView: function(full) {
    return this.inHorizontalView(full) && this.inVerticalView(full);
}});

这是我的纯JavaScript解决方案,如果它隐藏在一个可滚动的容器。

演示在这里(尝试调整窗口的大小)

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
};

编辑2016-03-26:我已经更新了解决方案,以考虑滚动过去的元素,所以它隐藏在可滚动容器的顶部。 编辑2018-10-08:更新到当滚动到屏幕上方的视图外时处理。

在毫无成效地跑来跑去并使用了几个不工作的代码之后。这就是我使用Jquery实现垂直滚动可视性的方法。 将'#footerplace'替换为您想垂直跟踪的元素。

jQuery.expr.filters.offscreen = function(el) {
  var rect = el.getBoundingClientRect();
  console.log(rect)
  console.log('window height', $(window).height());

  return (
           (rect.top <= $(window).height()) && (rect.bottom <= $(window).height())
         );
};
$(document).scroll(function(){
    if ($('#footerplace').is(':offscreen')){
      console.log('this is true');
    $('#footerplace').is(':offscreen');
    } else {
     console.log('this is false');
    $('#footerplace').is(':offscreen');

    }

这个答案的一个更有效的版本:

 /**
 * 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);
 }

制作了一个简单的插件,用于检测元素在可滚动容器中是否可见

    $.fn.isVisible = function(){

      var win;
      if(!arguments[0])
      {
        console.error('Specify a target;');
        return false;
      }
      else
      {
        win = $(arguments[0]);
      }
      var viewport = {};
      var bounds = this.offset();
      bounds.right = bounds.left + this.outerWidth();
      bounds.bottom = bounds.top + this.outerHeight();
      viewport.bottom = win.height() + win.offset().top;
      return (!( bounds.top > viewport.bottom) && (win.offset().top < bounds.bottom));
    };

像这样调用$('elem_to_check').isVisible('scrollable_container');

希望能有所帮助。