jQuery .data()如何工作的问题 [英] JQuery .data() how to work question

问题描述

我对.data()有疑问.在stackoverflow答案中，jquery将数据保存在缓存对象中，在缓存对象中以dom元素的哈希作为后缀.例如，将元素视为:

I have a question about .data(). In a stackoverflow answer, jquery saves data in cache object where cache index is suffixed with a hash of the dom element. For example, consider an element as:

1. #result ID，
2. 在Jquery缓存的第3个索引中
3. 并带有一个键:"carModel"&&值:奥迪"

现在，我阅读了.data()将键值与结果ID的哈希值和缓存索引一起保存.现在我的问题是，jQuery如何哈希dom中的任意元素?

Now, I read .data() will save the key-value with a hash value of result ID and cache index. Now my question is how jquery hash an arbitrary element in dom?

例如，考虑以下html:

For example, consider the following html:

<div id="begin"> 
  <p id="hello">Hello World</p>
  <p id="another">another</p>
  <div> <p>
      test p
    </p>
  </div>
  <p id="last">last</p>
<div>

为每个值分配一个值的代码:

Code to assign a value to each:

var i=0;

$("p").each( function() {
  $(this).data("value",i);
  ++i;

});

最后，让我们检索最里面的p元素的值:

Lastly, let's retrieve inner most p element's value:

alert( $("div div p").data("value") );
// output correctly => 2

---

我想知道它是如何工作的? :-)我的意思是说，jquery如何对元素进行哈希处理，从而可以在没有明确标识符(例如element-ID)的情况下检索它们?

---

I want to know how this works? :-) I mean how jquery hashed elements in such a way where they can be retrieved without definite identifier (like element-ID) to them?

感谢您的帮助...

推荐答案

jQuery数据的工作方式是将内部的所有数据存储在名为cache的变量中.每个jQuery会话都会创建一个扩展"，基本上是一个随机字符串，如jquery161362319162特定于该会话.将其放置在DOM中的每个对象(例如element.jquery161362319162)上，并在缓存中添加索引的值.

The way in which jQuery data works is by storing all the data internal in a variable called cache. Each jQuery session creates a "expando" which is basically a random string like jquery161362319162 specific to that session. This is placed on each object in the DOM such as element.jquery161362319162 with a value of the index in cache.

这是一个大致的工作原理示例.要在一个元素上添加对多个数据的支持，还需要做更多的工作，但是您将了解它在内部如何工作.

Here is a very basic example of roughly how it works. This will need a bit more work to add support for multiple data on an element, but you'll get the idea of how it works internally.

var cache = []; // Stores all the data for each element
var uid = 'jquery89437507043'; // random generated id,
                               // jQuery uses a function to automatically
                               // generate such a value

function data(element, key, data)
{
    if (data !== undefined) // We are setting data
    {
        var thisCache[key] = data;
        cache.push(thisCache)
        element[uid] = cache.length; // Place the index cache
                                        // for this data set on the element
    }
    else
    {
        return cache[element[uid]][key];
    }
}

用法

var div = $('div').get(0);
data(div, 'test', { 'apple': 'juice' });

alert(data(div, 'test').apple); // Will alert 'juice'

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