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jQuery scrollFix滾動定位插件
編輯:關於JavaScript     

當用戶向上或向下滾動頁面到一定位置時,目標元素開始固定定位(position:fixed),當回滾到原位置時目標元素恢復到原狀態,可以定制觸發滾動相對屏幕位置和觸發滾動方向,兼容IE6

【插件參數】

$(".target_element").scrollFix( [ "top" | "bottom" | length(可以為負,表示相對bottom), [ "top" | "bottom" ] ]);

第一個參數: 可選,默認為"top",當目標元素到了屏幕相對的位置時開始觸發固定,可以填一個數值,如100,-200 ,負值表示相對於屏幕下方

第一個參數: 可選,默認為"top",表示觸發固定的滾動方向,"top"表示從上向下滾動時觸發,"bottom"表示從下向上滾動時觸發

【下載插件】scrollFix(jb51.net).rar

復制代碼 代碼如下:
<script type="text/javascript" src="jquery-1.7.2.min.js"></script>
<script type="text/javascript" src="scrollFix.js"></script>
<p><span style="color: #808000;">【代碼示例】</span></p>
<div class="d">
<div class="demo" style="background: #ff6000;">$("#a").scrollFix(-200);
<div>滾動到距離下面200px時開始固定,默認從上到下觸發</div>
</div>
 </div>
<div class="d">
<div class="demo" style="background: #82BF00;">$("#b").scrollFix(200,"bottom");
<div>滾動到距離上面200px時開始固定,指定"bottom"從下到上觸發</div>
</div>
 </div>
<div class="d">
<div class="demo" style="background: #0C9CAE;">$("#c").scrollFix("top","top");
<div>滾動到距離上面0時開始固定,指定"top"從上到下觸發</div>
</div>
 </div>
<div class="d">
<div class="demo" style="background: #478FCE;">$("#d").scrollFix("bottom","top");
<div>滾動到距離下面0時開始固定,指定"bottom"從下到上觸發</div>
</div>
</div>

實現代碼:
復制代碼 代碼如下:
<script type="text/javascript">// <![CDATA[
window.onload=function(){
  $(".demo:eq(0)").scrollFix(-200);
  $(".demo:eq(1)").scrollFix(200,"bottom");
  $(".demo:eq(2)").scrollFix("top","top");
  $(".demo:eq(3)").scrollFix("bottom","bottom");
}
// ]]></script>

核心代碼:

;(function($) {
 jQuery.fn.scrollFix = function(height, dir) {
  height = height || 0;
  height = height == "top" ? 0 : height;
  return this.each(function() {
   if (height == "bottom") {
    height = document.documentElement.clientHeight - this.scrollHeight;
   } else if (height < 0) {
    height = document.documentElement.clientHeight - this.scrollHeight + height;
   }
   var that = $(this),
    oldHeight = false,
    p, r, l = that.offset().left;
   dir = dir == "bottom" ? dir : "top"; //默認滾動方向向下
   if (window.XMLHttpRequest) { //非ie6用fixed


    function getHeight() { //>=0表示上面的滾動高度大於等於目標高度
     return (document.documentElement.scrollTop || document.body.scrollTop) + height - that.offset().top;
    }
    $(window).scroll(function() {
     if (oldHeight === false) {
      if ((getHeight() >= 0 && dir == "top") || (getHeight() <= 0 && dir == "bottom")) {
       oldHeight = that.offset().top - height;
       that.css({
        position: "fixed",
        top: height,
        left: l
       });
      }
     } else {
      if (dir == "top" && (document.documentElement.scrollTop || document.body.scrollTop) < oldHeight) {
       that.css({
        position: "static"
       });
       oldHeight = false;
      } else if (dir == "bottom" && (document.documentElement.scrollTop || document.body.scrollTop) > oldHeight) {
       that.css({
        position: "static"
       });
       oldHeight = false;
      }
     }
    });
   } else { //for ie6
    $(window).scroll(function() {
     if (oldHeight === false) { //恢復前只執行一次,減少reflow
      if ((getHeight() >= 0 && dir == "top") || (getHeight() <= 0 && dir == "bottom")) {
       oldHeight = that.offset().top - height;
       r = document.createElement("span");
       p = that[0].parentNode;
       p.replaceChild(r, that[0]);
       document.body.appendChild(that[0]);
       that[0].style.position = "absolute";
      }
     } else if ((dir == "top" && (document.documentElement.scrollTop || document.body.scrollTop) < oldHeight) || (dir == "bottom" && (document.documentElement.scrollTop || document.body.scrollTop) > oldHeight)) { //結束
      that[0].style.position = "static";
      p.replaceChild(that[0], r);
      r = null;
      oldHeight = false;
     } else { //滾動
      that.css({
       left: l,
       top: height + document.documentElement.scrollTop
      })
     }
    });
   }
  });
 };
})(jQuery);
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