请在此 jQuery 代码中解释偏移函数的上下文答案

【问题标题】：Please explain context for the offset function in this jQuery code请在此 jQuery 代码中解释偏移函数的上下文
【发布时间】：2013-08-13 06:04:30
【问题描述】：

我正在尝试使用 jQuery 航点设置一些很酷的效果。但我不太擅长 javascript/jQuery。我对PHP比较熟悉。

航点代码提供基于页面滚动的触发事件。在下面的代码中，我使用了他们的“sticky”选项，它只是应该在窗口滚动超过某个点时将匹配元素的类设置为“stuck”。

所以，显然，在“粘性”之后，我可以传入一些用大括号括起来的选项。我希望根据元素相对于具有同一类的其他元素的位置来触发航点 (.example-basic)。第一个元素将在 0 处触发（当窗口碰到元素顶部时），第二个元素将在窗口离开元素顶部 N 时触发，其中 N 是前一个元素的高度。

我发现的最大问题是变量current 被设置为-1。我无法在列表中得到它的顺序。我猜offset: function 不知道this 是什么。如何让它工作？

$('.example-basic').waypoint('sticky',
        { offset: function() {
            var current = $('.example-basic').index(this);
            console.log('sticky Current index: ' + current);
            var total = 0;
            for(var i=0; i<current;i++) {
                total += heights[ i ];
            }
            /*var total = 0;
            $('.stuck').each( function(index, value) {
                total -= $(value).height();
            });*/
            console.log('Total: ' + total);
            return total;
            /*var total = 0;
            $('.stuck').each( function(index, value) {
                total -= $(value).height();
            });
            return total;*/
        }
    });

编辑：完整脚本（包括 CSS、HTML 和 javascript/jQuery）（我用 php echo 循环替换了一些重复的 HTML）

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<script src="http://code.jquery.com/jquery-latest.min.js"></script>
<script src="/includes/js/waypoints/waypoints.min.js"></script>
<script src="/includes/js/waypoints/shortcuts/sticky-elements/waypoints-sticky.js"></script>
<script type="text/javascript">
/*$(document).ready(function(direction) {
    $('#testing-waypoints').waypoint(function() {
        notify('Direction is ' + direction);
    });
});*/
/*$(function() {
    var notify = function(message) {
      var $message = $('<p style="display:none;">' + message + '</p>');

      $('.notifications').append($message);
      $message.slideDown(300, function() {
        window.setTimeout(function() {
          $message.slideUp(300, function() {
            $message.remove();
          });
        }, 2000);
      });
    };
});*/
$(document).ready(function(direction) {
    var notify = function(message) {
        var $message = $( message );
        if(direction == 'down') {
            $('.notifications').append($message);
            /* $message.slideDown(300, function() {
                window.setTimeout(function() {
                $message.slideUp(300, function() {
                $message.remove();
                  });
                }, 2000);
              });*/
        }
    };
    var heights = [];
    $('.example-basic').each( function(index, value) {
        heights[ index ] = $(value).height();
    });
    console.log('Heights: ' + heights);
    $('.example-basic').waypoint(function(direction) {

    $('.example-basic').waypoint('sticky',
        { offset: function() {
            console.log(this);
            console.log($(this));
            /*var first = $(this).children.first();*/
            var first = $('.example-basic').index($(this).children().first());
            console.log('first: ');
            console.log(first);
            /*var current = $('.example-basic').index(this);*/
            var current = first;
            var total = 0;
            for(var i=0; i<current;i++) {
                total += heights[ i ];
            }
            /*var total = 0;
            $('.stuck').each( function(index, value) {
                total -= $(value).height();
            });*/
            console.log('Total: ' + total);
            return total;
            /*var total = 0;
            $('.stuck').each( function(index, value) {
                total -= $(value).height();
            });
            return total;*/
        }
    });
    /*$('.stuck').each( function(index, value) {

    });*/



        if(direction == 'down') {
            /*notify($(this));*/
            $('#stuck-elements-wrapper').append($(this).clone());
            $(this).hide();
        } else {
            /*$('#stuck-elements-wrapper div:last-child').remove();*/
            $('#stuck-elements-wrapper').children().last().remove();
            $(this).show();
        }

    }, { offset: function() {
            var current = $('.example-basic').index(this);
            console.log('Current index: ' + current);
            var total = 0;
            for(var i=0; i<current;i++) {
                total += heights[ i ];
            }
            /*var total = 0;
            $('.stuck').each( function(index, value) {
                total -= $(value).height();
            });*/
            console.log('Total: ' + total);
            return total;
        }
    });
});
</script>
<style type="text/css">
.example-basic {
    border: 1px solid black;
    height: auto;
    width: 900px;
    text-align:center;
}
#stuck-elements-wrapper {
    position: fixed;
    z-index:25;
    height:0;
    overflow:visible;
    left:0;
    right:0;
    top:0px;
}
.stuck {
    position:relative;
    background-color:white;
}

</style>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
</head>

<body>
<div id="stuck-elements-wrapper" class="notifications">
</div>
<div class="container">
        <h1>jQuery Stick &lsquo;em</h1>

        <div class="row stickem-container">
            <div class="content">
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
            </div>

            <div id="testing-waypoints" class="aside stickem">
                <h2>Testing Waypoints</h2>
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
            </div>
        </div>

        <div class="row stickem-container">
            <div class="content">
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
            </div>

            <div class="aside stickem">
                <h2>Heading</h2>
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
            </div>
        </div>
<div class="example-basic" style="height:auto">
<p>Testing</p>
<p>2nd p tag</p>
</div>


        <div class="row stickem-container">
                <div class="content">
                    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
                    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
                    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
                    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
                </div>

                <div class="aside stickem">
                    <h2>Heading</h2>
                    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
                </div>
            </div>
            <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
            <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
            <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
            <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>

<?php
foreach(array(range(1,15) as $index) {
echo '<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>';
}
?>
  <?php
foreach(array(range(1,15) as $index) {
echo '<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>';
}
?>
    </div>
        <div class="example-basic">
    <p>Testing 2</p>
    </div>

    <div class="row stickem-container">
                <div class="content">
                    <?php
foreach(array(range(1,15) as $index) {
echo '<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>';
}
?>
                </div>

                <div class="aside stickem">
                    <h2>Heading</h2>
                    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
                </div>
            </div>
            <?php
foreach(array(range(1,15) as $index) {
echo '<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>';
}
?>
        </div>

    </body>
    </html>

【问题讨论】：

标签： jquery closures this jquery-context

【解决方案1】：

您的问题是偏移函数中的this 不是实际的example-basic div，而是航点创建的sticky-wrapper div。所以它在索引函数中不匹配。做：

console.log(this);

在函数的顶部看到，一旦你知道它相对容易你只需要获取内部元素，一种方法是：

var current = $('.example-basic').index($(this).children().first());

获取包装器 div 的第一个子元素，这就是你想要的。这似乎为我生成了正确的 current 值。

我不确定这是否是最快的方法，也许

var current = $('.example-basic').index($(this).children(':first-child'));

更清晰。您可能需要进行一些实验。

【讨论】：

我不是很在意时间，因为我从未目睹过明显缓慢的 jQuery 脚本。但是当我尝试您的解决方案时，当我向下滚动到第一个目标 div 时，浏览器完全冻结了。我现在已经发布了整个脚本（一些 HTML 部分被 PHP 回显循环替换以节省空间）。如果您能说出问题所在，我将不胜感激。谢谢。
您问题的格式已损坏，但我明白了。问题是航点处理程序函数（不是粘性处理程序）的无限循环。如果您在$('.example-basic').waypoint(function(direction) ... 之后将控制台日志放在该函数的顶部，您可以看到这一点。我怀疑这是在内部编辑航点功能而不是我所做的更改的问题。你想达到什么效果？
事实上，从路点处理函数内部对 any 元素调用.waypoint() 函数会导致无限循环。这看起来是由于插件的实现方式，您可能需要一种不同的方法（涉及首先设置所有内容，然后更改设置），而不是尝试动态更改功能。
感谢您的提示。我想我可能错误地将第二个航路点放在第一个航路点内。它们允许您将多个航点附加到任何元素。我只是将内部航路点功能移到了外部，就在外部航路点功能的上方，现在情况好多了。干得好，先生。再次感谢。