图片的预加载

昨天碰到个问题，页面要预先加载几张图片，于是直接在某个display:none的div中加了几个img，这样在页面加载的时候图片也加载了，后来发现这样在页面打开时太慢，就用jquery的load('src')方法在页面加载完成的时候去取图片

 

结果今天早上发现原来img是可以new的,new Image是可以产生一个image的dom对象的，然后为这个image指定src就OK了，

 

让我惊奇的是居然有dom对象是可以new出来的，一查原来还有一个Option也是可以new的，找了一些资料，说是dom对象都是对应一个接口的，一般是不能new的，但是也有例外,

 

下面的段落引用至：http://msdn.microsoft.com/en-us/library/dd282900

With Internet Explorer 8 running in IE8 standards mode, each DOM instance (such as window, document, event, and so on) has a corresponding interface object and interface prototype object. However, these objects differ from their JavaScript analogs in the following ways:

Interface objects

Interface objects generally do not have "constructor" functionality (cannot create a new DOM instance by using the JavaScript new operator). Exceptions include a few interface objects shipped in previous versions of Internet Explorer:

Option (alias for HTMLOptionElement)
Image (alias for HTMLImageElement)
XMLHttpRequest
XDomainRequest, which is new to Internet Explorer 8
The "prototype" property of interface objects may not be replaced (changed). An interface object's prototype property cannot be assigned a different interface prototype object at run-time.

Interface prototype objects

Interface prototype objects define the properties available to all DOM instances, but these built-in properties cannot be permanently replaced (e.g., the JavaScript delete operator will not remove built-in properties).

Other subtle but important differences are called out near the end of this article.