dropdown.js

/* ========================================================================
 * Bootstrap: dropdown.js v3.2.0
 * http://getbootstrap.com/javascript/#dropdowns
 * ========================================================================
 * Copyright 2011-2014 Twitter, Inc.
 * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
 * ======================================================================== */


+function ($) {
  'use strict';

  // DROPDOWN CLASS DEFINITION
  // =========================

  // as a click area for closing dropdown menus when clicking outside the menu.
  var backdrop = '.dropdown-backdrop';
  
  // attribute is relied on for closing dropdown menus at an application level, so it's a good idea to always use it.
  var toggle   = '[data-toggle="dropdown"]';


  var Dropdown = function (element) {
    $(element).on('click.bs.dropdown', this.toggle)
  }

  Dropdown.VERSION = '3.2.0'

  Dropdown.prototype.toggle = function (e) {
    var $this = $(this);
    // :disable 表单对象属性过滤选择器
    if ($this.is('.disabled, :disabled')) return;

    var $parent  = getParent($this);
    var isActive = $parent.hasClass('open');

    clearMenus()

    if (!isActive) {
      if ('ontouchstart' in document.documentElement && !$parent.closest('.navbar-nav').length) {
        // if mobile we use a backdrop because click events don't delegate
        $('<div class="dropdown-backdrop"/>').insertAfter($(this)).on('click', clearMenus)
      }

      var relatedTarget = { relatedTarget: this }
      $parent.trigger(e = $.Event('show.bs.dropdown', relatedTarget))

      if (e.isDefaultPrevented()) return

      $this.trigger('focus')

      $parent
        .toggleClass('open')
        .trigger('shown.bs.dropdown', relatedTarget)
    }

    return false
  }

  Dropdown.prototype.keydown = function (e) {
    if (!/(38|40|27)/.test(e.keyCode)) return

    var $this = $(this)

    e.preventDefault()
    e.stopPropagation()

    if ($this.is('.disabled, :disabled')) return

    var $parent  = getParent($this)
    var isActive = $parent.hasClass('open')

    if (!isActive || (isActive && e.keyCode == 27)) {
      if (e.which == 27) $parent.find(toggle).trigger('focus')
      return $this.trigger('click')
    }

    var desc = ' li:not(.divider):visible a'
    var $items = $parent.find('[role="menu"]' + desc + ', [role="listbox"]' + desc)

    if (!$items.length) return

    var index = $items.index($items.filter(':focus'))

    if (e.keyCode == 38 && index > 0)                 index--                        // up
    if (e.keyCode == 40 && index < $items.length - 1) index++                        // down
    if (!~index)                                      index = 0

    $items.eq(index).trigger('focus')
  }

  function clearMenus(e) {
    if (e && e.which === 3) return
    $(backdrop).remove()
    $(toggle).each(function () {
      var $parent = getParent($(this))
      var relatedTarget = { relatedTarget: this }
      if (!$parent.hasClass('open')) return
      $parent.trigger(e = $.Event('hide.bs.dropdown', relatedTarget))
      if (e.isDefaultPrevented()) return
      $parent.removeClass('open').trigger('hidden.bs.dropdown', relatedTarget)
    })
  }

  function getParent($this) {
    var selector = $this.attr('data-target');

    if (!selector) {
      selector = $this.attr('href')

	  /**
	   *        gist 咀嚼             
	   *
	   *  1.  #[A-Za-z] id 选择器
	   *  
	   *  2.  /.*(?=#[^\s]*$)/   这个表达式是为了选择 `#id` 选择器前面的空格。
	   *      (?=xxx) 意为匹配 xxx 之前的字符。
	   * 
	   *  3. 所以,全面的看来,若 selector 为 空, 直接返回 false;
	   *     只有最有一个之前的表达式为真时，才会返回最后一个表达式结果；
	   *     如遇当前表达式为假，后续不再执行。
	   * 
	   *  4. selector 不为空, 并且为 id(#xx) 选择器, 在后在替换掉 id 前的空格,返回选择符号
	   */ 
      selector = selector && /#[A-Za-z]/.test(selector) && selector.replace(/.*(?=#[^\s]*$)/, '') // strip for ie7
    }

    var $parent = selector && $(selector);

    return $parent && $parent.length ? $parent : $this.parent();
  }


  // DROPDOWN PLUGIN DEFINITION
  // ==========================

  function Plugin(option) {
    return this.each(function () {
      var $this = $(this)
      var data  = $this.data('bs.dropdown')

      if (!data) $this.data('bs.dropdown', (data = new Dropdown(this)))
      if (typeof option == 'string') data[option].call($this)
    })
  }

  var old = $.fn.dropdown

  $.fn.dropdown             = Plugin
  $.fn.dropdown.Constructor = Dropdown


  // DROPDOWN NO CONFLICT
  // ====================

  $.fn.dropdown.noConflict = function () {
    $.fn.dropdown = old
    return this
  }


  // APPLY TO STANDARD DROPDOWN ELEMENTS
  // ===================================

  $(document)
    .on('click.bs.dropdown.data-api', clearMenus)
    .on('click.bs.dropdown.data-api', '.dropdown form', function (e) { e.stopPropagation() })
    .on('click.bs.dropdown.data-api', toggle, Dropdown.prototype.toggle)
    .on('keydown.bs.dropdown.data-api', toggle + ', [role="menu"], [role="listbox"]', Dropdown.prototype.keydown)

}(jQuery);