some progress on affix plugin

js/bootstrap-affix.js

@@ -0,0 +1,102 @@
+/* ==========================================================
+ * bootstrap-affix.js v2.1.0
+ * http://twitter.github.com/bootstrap/javascript.html#affix
+ * ==========================================================
+ * Copyright 2012 Twitter, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * ========================================================== */
+
+
+!function ($) {
+
+  "use strict"; // jshint ;_;
+
+
+ /* AFFIX CLASS DEFINITION
+  * ====================== */
+
+  var Affix = function (element, options) {
+    this.options = $.extend({}, $.fn.affix.defaults, options)
+    this.$window = $(window)
+      .on('scroll.affix.data-api', $.proxy(this.checkPosition, this))
+      .on('resize.affix.data-api', $.proxy(this.refresh, this))
+    this.$element = $(element)
+    this.refresh()
+  }
+
+  Affix.prototype.refresh = function () {
+    this.position = this.$element.offset()
+  }
+
+  Affix.prototype.checkPosition = function () {
+    if (!this.$element.is(':visible')) return
+
+    var scrollLeft = this.$window.scrollLeft()
+      , scrollTop = this.$window.scrollTop()
+      , position = this.position
+      , offset = this.options.offset
+      , affix
+
+    if (typeof offset != 'object') offset = { x: offset, y: offset }
+
+    affix = (offset.x == null || (position.left - scrollLeft <= offset.x))
+         && (offset.y == null || (position.top  - scrollTop  <= offset.y))
+
+    if (affix == this.affixed) return
+
+    this.affixed = affix
+
+    this.$element[affix ? 'addClass' : 'removeClass']('affix')
+  }
+
+
+ /* AFFIX PLUGIN DEFINITION
+  * ======================= */
+
+  $.fn.affix = function (option) {
+    return this.each(function () {
+      var $this = $(this)
+        , data = $this.data('affix')
+        , options = typeof option == 'object' && option
+      if (!data) $this.data('affix', (data = new Affix(this, options)))
+      if (typeof option == 'string') data[option]()
+    })
+  }
+
+  $.fn.affix.Constructor = Affix
+
+  $.fn.affix.defaults = {
+    offset: 0
+  }
+
+
+ /* AFFIX DATA-API
+  * ============== */
+
+  $(function () {
+    $('[data-spy="affix"]').each(function () {
+      var $spy = $(this)
+        , data = $spy.data()
+  
+      data.offset = data.offset || {}
+
+      data.offsetX && (data.offset.x = data.offsetX)
+      data.offsetY && (data.offset.y = data.offsetY)
+
+      $spy.affix(data)
+    })
+  })
+
+
+}(window.jQuery);