javascript - 了解 Dean Edwards 的附加事件 JavaScript

Question

我需要帮助来理解这段代码。 handler.guid 有什么意义？为什么需要哈希表？

有什么意义:

if ( element["on" + type])
  {
  handlers[0] = element["on" + type];
  }

handleEvent 中的“this”是指元素还是 addEvent 函数？

function addEvent(element, type, handler) 
  {
  // assign each event handler a unique ID
  if (!handler.$$guid) handler.$$guid = addEvent.guid++;

  // create a hash table of event types for the element
  if (!element.events) element.events = {};

  // create a hash table of event handlers for each element/event pair
  var handlers = element.events[type];

  if (!handlers) 
    {
    handlers = element.events[type] = {};
    // store the existing event handler (if there is one)
    if (element["on" + type]) 
      {
      handlers[0] = element["on" + type];
      }
    }

  // store the event handler in the hash table
  handlers[handler.$$guid] = handler;

  // assign a global event handler to do all the work
  element["on" + type] = handleEvent;
  }

// a counter used to create unique IDs
addEvent.guid = 1;


function removeEvent(element, type, handler) 
  {
  // delete the event handler from the hash table
  if (element.events && element.events[type]) 
    {
    delete element.events[type][handler.$$guid];
    }
  }


function handleEvent(event) 
  {
  // grab the event object (IE uses a global event object)
  event = event || window.event;

  // get a reference to the hash table of event handlers
  var handlers = this.events[event.type];

  // execute each event handler
  for (var i in handlers) 
    {
    this.$$handleEvent = handlers[i];
    this.$$handleEvent(event);
    }
  }

Answer 1

guid用于给每个事件一个唯一的索引，而哈希表用于实现一个dynamic dispatch table。 . this.$$handleEvent 引用处理程序映射表中的元素。

回调系统通过将事件处理程序存储在数组中来工作。当检测到底层事件时，调度系统循环遍历数组，依次调用回调函数。

jQuery Event对象使用类似的结构。

引用资料

• A Few Words on GUIDs
• When Should I Use a Dispatch Table
• Delegating All of the Things With Ruby Forwardable - Words and Code
• The Gang of Four is wrong and you don't understand delegation — Saturn Flyer
• GUIDs and UUIDs
• RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace