jQuery - 滚动时更改背景颜色

Question

我想在滚动时转换固定标题元素的背景颜色.因此,当用户向下滚动整页块网站时,标题会巧妙地改变以补充块颜色.我几乎已经在Pen上实现了这一点,但是我无法确定如何测量已滚动多少作为何时更改的标志.

一些额外信息:要更改的滚动量为400px.背景颜色以数组形式存储和提取.作为参考我的jQuery代码如下:

$(document).ready(function(){
  var bgArray = ["#252525","#333333","#454545","#777777"];  
  var scrollHeight = 400;
  var scrolled = $(window).scrollTop(); //What is this measuring?

  $(window).scroll(function() { //Can these conditions be neatened into one function?
    if(scrolled < scrollHeight) {
      $('header').css('background', bgArray[0]);
    }
    if(scrolled > scrollHeight) { // i.e more than 400px
      $('header').css('background', bgArray[1]);
    }
    // and so on (800, 1200...)
  })
})

有关完整代码,请参阅笔.任何建议都非常感谢!

Answer 1

检查background每个header窗口的滚动程度(header)如下:

$(function() {
  var $header = $('header'),
    $window = $(window),
    bgArray = ["#252525", "red", "blue", "green"],
    headerHeight = 50,
    sectionHeight = 400;

  $window.scroll(function() {
    $header.css('background', bgArray[Math.floor(($header.offset().top + headerHeight)
        / sectionHeight)]);
  });
});

(所以现在我们可以使用它来改变进入块的颜色)

见下面的演示:

:root {
  --header: 50px; /* header height */
  --block: 400px; /* block height */
}

* {
  box-sizing: border-box; /* include padding in width / height calculations */
}

body {
  margin: 0; /* reset default margin of body */
}

header {
  height: var(--header); /* sets height of header */
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  color: #FFF;
  padding: 12px 0;
  background: #252525; /* initial background */
  transition: background 1s ease;
}

.container {
  margin: 0 auto;
}

.wrap>div {
  height: var(--block); /* sets height of each block */
  text-align: center;
}

p {
  margin: 0; /* reset margin of p */
}

.block-1 {
  background: #27AACC;
  color: #FFF;
}

.block-2 {
  background: #668E99;
  color: #FFF;
}

.block-3 {
  background: #4AFFC1;
  color: #444;
}

.block-4 {
  background: #FF8F8A;
  color: #FFF;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<header>
  <div class="container">
    Website Title.
  </div>
</header>

<div class="wrap">
  <div class="block-1">
    <div class="container">
      <p>This pen was made to solve a problem on a project...</p>
    </div>
  </div>
  <div class="block-2">
    <div class="container">
      <p>...I needed a sticky header with thr right bg colour.</p>
    </div>
  </div>
  <div class="block-3">
    <div class="container">
      <p>But this conflicted with the footer, which was the same colour...</p>
    </div>
  </div>
  <div class="block-4">
    <div class="container">
      <p>So the solution was to subtley change the header's bg on scroll</p>
    </div>
  </div>
</div>

$(document).ready(function() {
  var $header = $('header'),
    $window = $(window),
    bgArray = ["#252525", "#333333", "#454545", "#777777"],
    headerHeight = $header.outerHeight();

  $window.scroll(function() {
    for (var i = 1; i < 5; i++) {
      if ($window.scrollTop() + headerHeight > $('.block-' + i).offset().top) {
        $header.css('background', bgArray[i - 1]);
      }
    }
  });
});

Answer 2

您使用滚动作为固定变量,您应该在您的条件下直接使用它

这将使包装div内的所有元素动态化

$(document).ready(function(){
var bgArray = ["#252525","#333333","#454545","#777777"];
$(window).scroll(function() { 
    for(var i = 1; i < bgArray.length; i++) {
      if ($(window).scrollTop() > $('.wrap div:nth-child(' + i + ')').offset().top) {
        $('header').css('background', bgArray[i-1]);        
      }
    }
  });
})